OSA's Digital Library

Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 20 — Oct. 7, 2013
  • pp: 24219–24230
« Show journal navigation

High sensitivity UV fluorescence spectroscopy based on an optofluidic jet waveguide

Gianluca Persichetti, Genni Gesta, and Romeo Bernini  »View Author Affiliations


Optics Express, Vol. 21, Issue 20, pp. 24219-24230 (2013)
http://dx.doi.org/10.1364/OE.21.024219


View Full Text Article

Acrobat PDF (2304 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

A novel spectroscopic sensor based on an optofluidic liquid jet waveguide is presented. In this device, a liquid jet waveguide is generated with the solution under analysis. This stream, exploiting total internal reflection, acts as an optical waveguide confining the autofluorescence light produced by chemical or biological samples when opportunely excited. Using a self-aligned configuration, the liquid jet is directly coupled with a multimode optical fiber collecting the fluorescence towards the detection system. Experimental measurements have been performed using an UV excitation source on water solutions containing representative water pollutants as aromatic hydrocarbons or bacteria showing very low limit of detection.

© 2013 OSA

1. Introduction

Fluorescence spectroscopy is a powerful and widely used tool in several areas as for instance biochemistry, material sciences, biophysics and environmental monitoring. Among possible approaches, techniques based on laser induced fluorescence (LIF) are very commonly used because of their well-known high sensitivity and selectivity. The ultimate sensitivity level has been reached, as different single molecule detection methods based on fluorescence spectroscopy are now available [1

1. W. E. Moerner and D. P. Fromm, “Methods of single-molecule fluorescence spectroscopy and microscopy,” Rev. Sci. Instrum. 74(8), 3597–3619 (2003). [CrossRef]

]. Fluorescence spectroscopy based on autofluorescence offers several benefits such as continuous online monitoring [2

2. R. K. Henderson, A. Baker, K. R. Murphy, A. Hambly, R. M. Stuetz, and S. J. Khan, “Fluorescence as a potential monitoring tool for recycled water systems: A review,” Water Res. 43(4), 863–881 (2009). [CrossRef] [PubMed]

] and no need for reagents or sample pretreatment by its own nature. In particular, autofluorescence excited by UV radiation allows to detect a very wide range of organic compounds ranging from aromatic hydrocarbons [3

3. P. Karlitschek, F. Lewitzka, U. Bünting, M. Niederkrüger, and G. Marowsky, “Detection of aromatic pollutants in the environment by using UV-laser-induced fluorescence,” Appl. Phys. B 67(4), 497–504 (1998). [CrossRef]

,4

4. D. Patra, “Applications and new developments in fluorescence spectroscopic techniques for the analysis of polycyclic aromatic hydrocarbons,” Appl. Spectrosc. Rev. 38(2), 155–185 (2003). [CrossRef]

] to bacterial cells [5

5. P. J. Hargis Jr, T. J. Sobering, G. C. Tisone, J. S. Wagner, S. A. Young, and R. J. Radloff, “Ultraviolet fluorescence identification of protein, DNA, and bacteria,” Proc. SPIE 2366, 147–153 (1995). [CrossRef]

,6

6. L. Leblanc and E. Dufour, “Monitoring the identity of bacteria using their intrinsic fluorescence,” FEMS Microbiol. Lett. 211(2), 147–153 (2002). [CrossRef] [PubMed]

].

The performances of sensors based on LIF depend essentially on the ratio between the collected fluorescent signal and the background signal. Several approaches have been proposed in order to optimize this signal-to-noise ratio also in microfluidic chips [7

7. B. Kuswandi, J. Nuriman, J. Huskens, and W. Verboom, “Optical sensing systems for microfluidic devices: a review,” Anal. Chim. Acta 601(2), 141–155 (2007). [CrossRef] [PubMed]

]. Optical waveguides with integrated microfluidics has been successfully applied enabling to integrate excitation system, waveguides and microfluidic channels on the same chip [8

8. C. Vannahme, S. Klinkhammer, U. Lemmer, and T. Mappes, “Plastic lab-on-a-chip for fluorescence excitation with integrated organic semiconductor lasers,” Opt. Express 19(9), 8179–8186 (2011). [CrossRef] [PubMed]

]. Recently, optofluidic waveguides have been proposed to increase the fluorescence collection efficiency [9

9. W. P. Risk, H. C. Kim, R. D. Miller, H. Temkin, and S. Gangopadhyay, “Optical waveguides with an aqueous core and a low-index nanoporous cladding,” Opt. Express 12(26), 6446–6455 (2004). [CrossRef] [PubMed]

11

11. S. Smolka, M. Barth, and O. Benson, “Highly efficient fluorescence sensing with hollow core photonic crystal fibers,” Opt. Express 15(20), 12783–12791 (2007). [CrossRef] [PubMed]

]. A rapidly growing field is also represented by optofluidic single molecule detection and imaging technique, which are frequently based on fluorescence detection [12

12. A. E. Vasdekis and G. P. J. Laporte, “Enhancing single molecule imaging in optofluidics and microfluidics,” Int. J. Mol. Sci. 12(12), 5135–5156 (2011). [CrossRef] [PubMed]

,13

13. J. Wu, G. Zheng, and L. M. Lee, “Optical imaging techniques in microfluidics and their applications,” Lab Chip 12(19), 3566–3575 (2012). [CrossRef] [PubMed]

]. However in these encouraging approaches for high sensitive measurements, all waveguides are inserted in a solid structure generating light scattering, coming from surface roughness of confining walls, and autofluorescence of non analyte materials that limit the sensor performances especially when UV excitation is used. Furthermore, the reliability of optical measurement is strongly influenced by the fouling of microchannel walls. In order to overcome these problems water jets, acting as an optical waveguide, have been recently proposed for LIF spectroscopy and the working principle has been tested [14

14. G. Persichetti, G. Testa, and R. Bernini, “Optofluidic jet waveguide for laser-induced fluorescence spectroscopy,” Opt. Lett. 37(24), 5115–5117 (2012). [CrossRef] [PubMed]

].

Despite a water stream offers unique properties such as waveguiding nature without surface roughness or a high numerical aperture (NA = 0.88) very few examples of application are known. Water-jets waveguides have been used in laser cutting device [15

15. B. Richerzhagen, “Chip singulation process with a water-jet guided laser,” Solid State Technol. 44, 25–28 (2001).

] or in liquid chromatography [16

16. S. Folestad, L. Johnson, B. Josefsson, and B. Galle, “Laser-induced fluorescence detection for conventional and microcolumn liquid chromatography,” Anal. Chem. 54(6), 925–929 (1982). [CrossRef]

] however, without fully exploiting the great advantage of this device. Moreover, the rare configurations proposed in literature require bulky optic and fluidic device with careful alignment procedure.

In this work the design and the application of an UV spectroscopic system based on a high speed liquid jet is reported for high sensitive detection of several chemical compound. The liquid jet (the solution to analyze) is generated by means of a stainless-steel needle housed in a polymethylmethacrylate (PMMA) structure. This stream, exploiting total internal reflection (TIR), acts as an optical waveguide for the fluorescence light produced by organic compounds dissolved within which are opportunely excited by means of an UV laser source. A self-aligned configuration allows direct coupling of the liquid jet with a multimode optical fiber which collects the fluorescence towards the detection system.

As several water pollutants are organic compounds, this sensor can be profitably used in environmental monitoring. The device is able to overcome the previously mentioned issues as no solid walls are used to surround the waveguide used to collect the fluorescence signal or to contain the solution to analyze.

2. Sensor design and fabrication

When a liquid is emitted from a round nozzle, the shape of the stream results from different forces acting on the liquid: the gravitational and the inertial force as also the viscous drag and the surface tension. Depending on the liquid velocity, different regimes can be identified. At low velocity the formation of droplets, characterized by a quasi-static balance between inertial and surface tension, will be observed. This is the so called dripping regime. Increasing the velocity above a certain critical value, such that the kinetic energy overcomes the surface energy, we have a jetting regime where a continuous jet formation is observed. The jet has a continuous shape forming a regular cylinder up to a certain length (named breakup length), and then it breaks up into drops. The breakup length first increases linearly with jet velocity reaching a maximum (linear regime) and then it begins to decrease until a minimum of the breakup length. A further increasing of the liquid velocity leads to a jet atomization. Since the 19th century, the stability and breakup of a liquid jet column has been extensively studied. However, well before the first investigation of this phenomenon [17

17. J. W. S. Rayleigh, “On the instability of jets,” Proc. Lond. Math. Soc. 10(1), 4–13 (1878). [CrossRef]

], the waveguiding nature of a water stream was discovered and explained as due to TIR at the water-air interface by Daniel Colladon [18

18. D. Colladon, “On the reflections of a ray of light inside a parabolic liquid stream,” CR (East Lansing, Mich.) 15, 800–802 (1842).

].

By exploiting TIR occurring in a water jet it has been possible to design a high sensitive spectroscopic sensor. The optofluidic sensor layout is illustrated in Fig. 1
Fig. 1 Schematic of the water jet waveguide sensor.
. In the proposed device, the solution to analyze is injected into a stainless-steel needle that acts as nozzle in order to produce a continuous liquid stream. The autofluorescence of the chemical compounds present in the solution is excited by means of an UV laser source impinging in orthogonal direction with respect to the liquid flow direction. The fluorescence light, experiencing total internal reflection, is efficiently guided by the liquid jet waveguide and subsequently delivered to the detection system by a multimodal optical waveguide which is co-axial with the liquid stream.

The advantages of this configuration rely on the intrinsic optical properties of the optofluidc jet waveguides which allow to overcome the typical drawbacks of conventional LIF experimental setup that make use of flow cells [19

19. R. J. van de Nesse, N. H. Velthorst, U. A. Th. Brinkman, and C. Gooijer, “Laser-induced fluorescence detection of native-fluorescent analytes in column liquid chromatography, a critical evaluation,” J. Chromatogr. A 704(1), 1–25 (1995). [CrossRef]

], microfluidic channel [20

20. P. C. H. Li, Microfluidic Lab-on-a-Chip for Chemical and Biological Analysis and Discovery (Taylor and Francis/CRC Press 2006), Chap. 7.

] or optofluidic waveguides [9

9. W. P. Risk, H. C. Kim, R. D. Miller, H. Temkin, and S. Gangopadhyay, “Optical waveguides with an aqueous core and a low-index nanoporous cladding,” Opt. Express 12(26), 6446–6455 (2004). [CrossRef] [PubMed]

11

11. S. Smolka, M. Barth, and O. Benson, “Highly efficient fluorescence sensing with hollow core photonic crystal fibers,” Opt. Express 15(20), 12783–12791 (2007). [CrossRef] [PubMed]

]. The surface tension of the liquid stream leads to a liquid/air boundary without any practical roughness except that stationary waves [21

21. K. M. Awati and T. Howes, “Stationary waves on cylindrical fluid jets,” Am. J. Phys. 64(6), 808–811 (1996).

] negligible in our regime. This circumstance together with the absence of solid walls minimize the background signal due to the scattering and the fluorescence of non analyte materials along the light path. In addition, the higher numerical aperture (NA = 0.88), offered by a water stream in air with respect to others liquid core waveguides [9

9. W. P. Risk, H. C. Kim, R. D. Miller, H. Temkin, and S. Gangopadhyay, “Optical waveguides with an aqueous core and a low-index nanoporous cladding,” Opt. Express 12(26), 6446–6455 (2004). [CrossRef] [PubMed]

,22

22. Y. Zhao, M. Jenkins, P. Measor, K. Leake, S. Liu, H. Schmidt, and A. R. Hawkins, “Hollow waveguides with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films,” Appl. Phys. Lett. 98(9), 091104 (2011). [CrossRef] [PubMed]

], enables to strongly increase the collection efficiency. Finally, this configuration avoids the fouling of microchannel walls that has significant implications in the reliability of microfluidic device and on the long term stability of the optical measurements. A thin Teflon AF coating on the collecting optical fiber could be used in order to avoid biofouling also on this optical component.

2.1 Sensor fabrication

The fabrication of the microfluidic sensor was performed by means of a high-precision micromilling machine. The device consists of two PMMA substrates (thickness of 4mm) milled in a “U” shape and joined by means of screws. In one layer a long channel with around 1.6 x 1.6 mm cross section was milled by an end tool with 1587.5 µm ± 12.7 μm diameter. The channel dimensions was chosen in order to hold two needles expressly designed for liquid chromatography. One needle is used as fluidic channel and the other one as groove for the collecting optical fiber. The “U” shape was used in order to have a wide open region where the liquid jet can flow without surrounding PMMA walls. This precaution prevents possible background fluorescence coming from the PMMA frame.

This configuration allows self-alignment between the water jet and the optical fiber. Both of the needles used in the device have an external diameter of 1587.5 µm, the upper one (used to produce the jet) has an internal diameter of 1016 µm, the lower needle has an internal diameter of 762 µm and it is used to hold a 600 µm core size solarization resistant optical fiber (NA = 0.22).

The velocity of the water stream used in the experiments was estimated as 1.4 m/s. The stream velocity controls the jet formation; furthermore it will also affect the sensitivity detection as the number of particle passing in the volume excited by the laser beam will depend on the jet velocity.

The generated stream diameter was 955 µm and the distance between the collecting optical fiber and the nozzle of the needle (i.e the liquid stream length) was 16 mm. The corresponding jet breakup length was measured as around 10 cm for a bi-distilled water stream. This value is in agreement with literature results and falls in the linear regime of the corresponding breakup curve [23

23. S. Rajendran, M. A. Jog, and R. M. Manglik, “Experimental investigation of liquid jet breakup at low Weber number” in ILASS Americas,24th Annual Conference on Liquid Atomization and Spray Systems, (San Antonio, TX, 2012), pp. 1–6.

].

A detail of the actual jet produced using the device is shown in Fig. 2
Fig. 2 Detail of the liquid jet sensor with liquid jet formed (a) and without (b).
where a regular jet shape is illustrated; for comparison it is also shown the same portion of the device without jet. The lower needle firmly holds the collecting optical fiber, avoiding any vibration. In the region where the jet falls on the optical fiber the TIR is always present, but it is reasonable to consider the occurrence of coupling losses similar to the one arising when two fiber with different diameter and NA are coupled.

2.2 Experimental setup

The detector used to analyze the autofluorescence of water pollutants was a low cost mini-spectrophotometer connected to a personal computer for the storage and the evaluation of the recorded spectra. The spectrometer used was a Hamamatsu TM C10083CA with a transmission holographic grating, slit width 70 µm and a spectral resolution of 8 nm. In order to reduce the wastage of the water solutions used to perform measurements, a low cost mini-pump (RS 480-188, maximum flow rate: 350ml/min) was used to realize a recirculation system. As the jet breakup length is certainly longer than the distance between the nozzle and the collecting optical fiber, possible variation of the pump flow rate did not affect the stream stability.

3. Fluorescence measurements

In order to test the device performances in the quantification of water pollutants, aqueous solutions containing representative pollutants as aromatic hydrocarbons or bacteria have been considered in concentration values ranging at least three orders of magnitude. Fluorescence measurements has been obtained considering an integration time of 5s. For each sample 40 repeated measurements have performed in order to produce adequate statistics. The calibration curve for each pollutant has been evaluated considering the integral of the detected optical intensity in the wavelength range where fluorescence was present. The limit of detection (LOD) has been calculated as three times of the standard deviation of the blank measurement (i.e. considering a pure water stream) according to the International Union of Pure and Applied Chemistry rules [24

24. J. Inczedy, T. Lengyel, and A. M. Ure, Compendium of analytical nomenclature. The orange book, 3rd edn., (Blackwell, Oxford 1998).

].

Preliminary measurements have been performed on bi-distilled water solutions in order to evaluate the background noise. A typical recorded spectrum is shown in Fig. 4
Fig. 4 Bi-distilled water spectrum used as blank measurement. The same measurement performed in a quartz cuvette is reported for comparison.
where it is possible to clearly distinguish the low contribution coming from the excitation source at 266 nm and the Raman peak of the water at 292 nm. The low residual pump contribution in the detected spectrum is achieved because of the surface tension of the liquid pulling the waveguide’s boundaries to smooth surfaces and thus avoiding surface scattering. In the same spectrum is evident a background fluorescence signal. This contribution is generally explained as originated from the presence of humic compounds. Humic substances are natural organic compounds contained in all natural waters but still present at low level in purified water [25

25. L. V. Belovolova, M. V. Glushkov, E. A. Vinogradov, V. A. Babintsev, and V. I. Golovanov, “Ultraviolet fluorescence of water and highly diluted aqueous media,” Phys. Wave Phenom. 17(1), 21–31 (2009). [CrossRef]

]. Even if the detection of this residual fluorescence can be considered as a sign of high level detector sensitivity, it also affects the signal to noise ratio leading to a deterioration in the achievable LOD. In order to show the improvement with respect conventional technique, in Fig. 4 it is also shown a similar measurement performed in a quartz cuvette (12.5 x 12.5 x 45 mm). The measurements was performed using the same excitation source and collecting the fluorescence (in orthogonal direction with respect the laser source) by means of the same optical fiber used in the jet waveguide sensor.

For a comparison of the collection efficiency between the two approaches it should be taken into account that excitation volume in cuvette is more than 80 times the one of the jet waveguide. The corresponding sensitivity enhancement was estimated as a factor of 160.

3.1 Organic compounds detection

Mono-aromatics hydrocarbons as benzene, toluene and xylene (collectively known as BTX) and polycyclic aromatic hydrocarbons (PAHs) play a significant role as water pollutants due to their carcinogenic and/or mutagenic potential. BTX compounds are highly toxic substances, thus forming one of the main groundwater and health-risk contaminant groups. They can easily reach groundwater as they are not strongly adsorbed to the soil and therefore, they are able to contaminate water supplies. PAHs are generated in any incomplete combustion process. The soil near tar production plants or gasworks is also frequently contaminated with PAHs. Monoaromatics (at trace levels also PAHs) are constituents of mineral oil products. Thus after oil spills, they can contaminate soil, surface water and, due to their high mobility, also groundwater. Some PAHs (e.g. naphthalene) have also been used in the synthesis of different organic compounds in fungicides, pesticides, dyes, detergents and mothballs [26

26. J. L. Shennan, “Hydrocarbons as substrates in industrial fermentation,” in Petroleum Microbiology R.M. Atlas, ed. (Macmillan Publishing Company, 1984).

]. For all these reasons PAHs have been listed by the US Environmental Protection Agency and the European Community as priority pollutants.

The first hydrocarbons detected was toluene; water solutions in concentration ranging from 0.032 to 25.19 ppm were used. Some illustrative spectra are shown in Fig. 5
Fig. 5 Fluorescence spectra of toluene in water at different concentration. Fluorescence spectrum of water is reported for comparison.
. In Fig. 6
Fig. 6 Calibration curve of the sensor for toluene water solution ranging from 0.032 to 25.19 ppm. As in the following plots the horizontal line is drawn considering three times the value of the standard deviation calculated on blank measurements. The LOD is 0.72 ppm.
the device calibration curve for water solutions of toluene is reported. Each point of the curve was calculated evaluating the integral of the optical intensity detected by the minispectrometer in the wavelength range (275–425) nm leading to a limit of detection of 0.72 ppm. In order to estimate the efficiency improvement with respect to conventional approach, measurement in the same experimental condition was also performed in a quartz cuvette by means of the same setup previously described. Normalizing to the same excitation volume, in the measurement performed using the jet waveguide (as it was previously observed in the measurements on water) it was estimated an enhancement of a factor of 30 with respect the results obtained in cuvette.

As it can be observed, the collected fluorescence intensity is directly proportional to the sample concentration for all the measured solutions.

Benzene water solutions in a concentration range from 0.049 ppm to 34.67 ppm was used to obtain the calibration curve for this molecule. The detected spectra were integrated between 275 and 425 nm in order to evaluate the fluorescence intensity in the useful wavelength range. The calibration curve for benzene water solutions and the linear behavior of the relationship between fluorescence intensity and concentration are shown in Fig. 7
Fig. 7 Calibration curves of the devices for benzene water solutions ranging from 0.49 to 34.64 ppm. The LOD is 1.94 ppm.
. The LOD found in this case was 1.94 ppm.

The other component of the BTX family has been the o-Xylene. Considering water solutions between 1.2 ppb and 0.69 ppm, an LOD of 0.1 ppm was found (see Fig. 8
Fig. 8 Calibration curves of the sensor for o-Xylene water solutions ranging from 0.0012 to 0.69 ppm. The LOD found for this molecule is 0.1 ppm.
). In this case the integral of the spectra was evaluated between 275 and 350 nm.

As example of PAH, naphthalene water solutions has been considered. In this case the concentration range examined was from 2.36∙10−4 to 0.13 ppm. Some example of the acquired spectra are reported in Fig. 9
Fig. 9 Fluorescence spectra of naphthalene in water at different concentration. Fluorescence spectrum of water is reported for comparison.
. The calibration curve, reported in Fig. 10
Fig. 10 Calibration curve of the sensor for naphthalene water solution ranging from 2.36∙10-4 to 0.13 ppm. The LOD is 2.2 ppb.
, was obtained considering integrals between 300 and 420 nm and the corresponding LOD was 0.0022 ppm.

3.2 Bacterial detection

As additional application of the sensor, performances on bacterial cells detection was evaluated. Cells of most organisms exhibit autofluorescence, because of the existence of numerous intracellular constituents including aromatic amino acids, NAD(P)H, flavins, and lipofuscins [27

27. N. Billinton and A. W. Knight, “Seeing the wood through the trees: A review of techniques for distinguishing green fluorescent protein from endogenous autofluorescence,” Anal. Biochem. 291(2), 175–197 (2001). [CrossRef] [PubMed]

].

In these measurements, an increasing of pump scattering contribution has been observed because of the bacteria cell themselves act as scatterers in the water solution. Due to the extent of the observed fluorescence region, the integrals for the evaluation of the LOD was calculated from 300 to 700 nm. Experimental measurements shown in Fig. 11
Fig. 11 Calibration curve for Bacillus subtilis solution. The LOD is 2.45∙105 bacteria/ml.
attest a limit of detection of 2.45∙105 bacteria/ml. This LOD corresponds to detect less than 2000 bacteria in the excited volume. In the same figure it is evident an excellent linear behavior of the fluorescence signal vs. bacteria concentration.

As previously underlined, the stream velocity affects the LOD value as the bacteria solution can be considered an inhomogeneous fluid containing discrete entities.

4. Discussion

The device performances in the quantification of water pollutants show that the device is potentially useful for environmental monitoring activity, especially for early warning systems, an application field the detector is particularly intended for. The reported LODs demonstrate that, despite the low quantum yield of the considered hydrocarbons in water (0.01-0.11) [30

30. R. Meidinger, R. W. St. Germain, V. Dohotariu, and G. D. Gillispie, Field Screening Methods for Hazardous Wastes and Toxic Chemicals (Air & Waste Management Association, 1993), Chap. Fluorescence of Aromatic Hydrocarbons in Aqueous Solutions.

], they can be detected by the jet waveguide sensor at concentrations often found in the environment, performing better results in comparison to devices proposed for same applications. For instance, a portable device based on fluorescence report an LOD of 100 ppm, 2 ppm and 0.8 ppm in [31

31. J. Sinfield, H. Hemond, J. Germaine, B. Johnson, and J. Bloch, “Contaminant detection, identification, and quantification using a microchip laser fluorescence sensor,” J. Environ. Eng. 133(3), 346–351 (2007). [CrossRef]

] respectively for benzene, toluene and o-xilene. In particular, the device is able to detect toluene and xylene below the highest allowed level in drinking water accordingly to the EPA “National Primary Drinking Water Regulations” which places as reference values 1 ppm for toluene and 10 ppm for total xylenes [32

32. U.S. Environmental Protection Agency, 2012Edition of the Drinking Water Standards and Health Advisories, EPA 822-S-12–001, http://water.epa.gov/action/advisories/drinking/upload/dwstandards2012.pdf.

]. The ability to detect aromatic compounds as BTX has an additional value as the presence of these molecules can be often considered as a strong signal of the occurrence of other aromatic compounds. As representative element of the PAHs group, naphthalene is detected at a very low limit of detection (2.2 ppb). A summary of the LODs estimated in the experimental measurements is listed in Table 1

Table 1. Summary of the LODs

table-icon
View This Table
where levels allowed in drinking water according to EPA regulations are also listed for comparison.

Investigation on detection and quantification on bacterial cells has been performed on Bacillus subtilis as simulant of Bacillus anthracis. An LOD of 2.45∙105 bacteria/ml is competitive also if compared to results obtained for Bacillus anthracis considering different detection approaches [29

29. A. B. Herzog, S. D. McLennan, A. K. Pandey, C. P. Gerba, C. N. Haas, J. B. Rose, and S. A. Hashsham, “Implications of limits of detection of various methods for Bacillus anthracis in computing risks to human health,” Appl. Environ. Microbiol. 75(19), 6331–6339 (2009). [CrossRef] [PubMed]

]. Considering the detection system used to perform the measurements, this encouraging value seems promising in further investigation on different microbial cells and also on the realization of a flow cytometer based on a different detection configuration.

In order to correctly evaluate the device performance, it should be taken into account that the current limit of detection is strongly influenced by the available detection system. In particular, the numerical aperture of the low cost mini-spectrophotometer (NA = 0.22) and the one of the collecting optical fiber (NA = 0.22) do not match the numerical aperture of a water stream (NA = 0.88). This means that the high collection efficiency achievable by means a water jet is not fully exploited, thus limiting the potential detector performances. The reason of such choice relies to its compact size allowing an easy portability of the device. This characteristic is a needful constraint of our system as it is intended as a first step to attain towards a portable device for in situ environmental monitoring activity. In order to improve the NA matching between the liquid jet and the detection system a suitable optical system could be designed for this purpose.

A simple strategy to additionally lowering the sensor LOD relies on a further increasing of the excited volume. In addition, in the actual device, the laser spot beam size is around 8 mm whereas the jet length is 16 mm. Using a cylindrical lens to reshape the output beam could excite more effectively the jet, leading to a further decrease of the LOD.

The proposed spectroscopic sensor was not expressly designed to discriminate among different chemical compounds or bacteria. Nevertheless a possible approach to allow discrimination among different organic compound or micro-organisms could be performed by means of principal component analysis (PCA) of the fluorescence spectra [6

6. L. Leblanc and E. Dufour, “Monitoring the identity of bacteria using their intrinsic fluorescence,” FEMS Microbiol. Lett. 211(2), 147–153 (2002). [CrossRef] [PubMed]

]. The use of multi-wavelength LED excitation could further increase the detection and the discrimination of mixture of different chemical compounds enabling also an increasing of the device compactness.

5. Conclusion

A liquid jet waveguide based spectroscopic sensor has been developed and successfully applied in detection of water pollutants as hydrocarbons and bacteria exploiting their natural fluorescence. The key component of this device is a water stream which acts as a waveguide and at the same, replaces the commonly used cuvettes or flow cells. The designed configuration allows a direct coupling with the optical fiber used to collect fluorescence arising from water pollutants and consequently a perfect integration with pigtail detectors. The configuration is also self-aligned, avoiding conventional alignment problem occurring when fiber optic components are used and systems are shock sensitive. Optical performances of the system are improved by the waveguiding nature of a water stream ensuring high collection efficiency of the fluorescence signal. The presented spectroscopic sensor does not require sample pretreatment and no complex data analysis is required. These characteristics in addition to its cheapness and compactness make it suitable as early warning system for water quality monitoring.

Acknowledgments

The research leading to these results has received funding from the Italian Ministero dello Sviluppo Economico, under Grant Agreement “Industria 2015 –New Technologies for the Made In Italy”, No. MIOl 00223 (project ACQUASENSE).

References and links

1.

W. E. Moerner and D. P. Fromm, “Methods of single-molecule fluorescence spectroscopy and microscopy,” Rev. Sci. Instrum. 74(8), 3597–3619 (2003). [CrossRef]

2.

R. K. Henderson, A. Baker, K. R. Murphy, A. Hambly, R. M. Stuetz, and S. J. Khan, “Fluorescence as a potential monitoring tool for recycled water systems: A review,” Water Res. 43(4), 863–881 (2009). [CrossRef] [PubMed]

3.

P. Karlitschek, F. Lewitzka, U. Bünting, M. Niederkrüger, and G. Marowsky, “Detection of aromatic pollutants in the environment by using UV-laser-induced fluorescence,” Appl. Phys. B 67(4), 497–504 (1998). [CrossRef]

4.

D. Patra, “Applications and new developments in fluorescence spectroscopic techniques for the analysis of polycyclic aromatic hydrocarbons,” Appl. Spectrosc. Rev. 38(2), 155–185 (2003). [CrossRef]

5.

P. J. Hargis Jr, T. J. Sobering, G. C. Tisone, J. S. Wagner, S. A. Young, and R. J. Radloff, “Ultraviolet fluorescence identification of protein, DNA, and bacteria,” Proc. SPIE 2366, 147–153 (1995). [CrossRef]

6.

L. Leblanc and E. Dufour, “Monitoring the identity of bacteria using their intrinsic fluorescence,” FEMS Microbiol. Lett. 211(2), 147–153 (2002). [CrossRef] [PubMed]

7.

B. Kuswandi, J. Nuriman, J. Huskens, and W. Verboom, “Optical sensing systems for microfluidic devices: a review,” Anal. Chim. Acta 601(2), 141–155 (2007). [CrossRef] [PubMed]

8.

C. Vannahme, S. Klinkhammer, U. Lemmer, and T. Mappes, “Plastic lab-on-a-chip for fluorescence excitation with integrated organic semiconductor lasers,” Opt. Express 19(9), 8179–8186 (2011). [CrossRef] [PubMed]

9.

W. P. Risk, H. C. Kim, R. D. Miller, H. Temkin, and S. Gangopadhyay, “Optical waveguides with an aqueous core and a low-index nanoporous cladding,” Opt. Express 12(26), 6446–6455 (2004). [CrossRef] [PubMed]

10.

A. Chen, M. M. Eberle, E. J. Lunt, S. Liu, K. Leake, M. I. Rudenko, A. R. Hawkins, and H. Schmidt, “Dual-color fluorescence cross-correlation spectroscopy on a planar optofluidic chip,” Lab Chip 11(8), 1502–1506 (2011). [CrossRef] [PubMed]

11.

S. Smolka, M. Barth, and O. Benson, “Highly efficient fluorescence sensing with hollow core photonic crystal fibers,” Opt. Express 15(20), 12783–12791 (2007). [CrossRef] [PubMed]

12.

A. E. Vasdekis and G. P. J. Laporte, “Enhancing single molecule imaging in optofluidics and microfluidics,” Int. J. Mol. Sci. 12(12), 5135–5156 (2011). [CrossRef] [PubMed]

13.

J. Wu, G. Zheng, and L. M. Lee, “Optical imaging techniques in microfluidics and their applications,” Lab Chip 12(19), 3566–3575 (2012). [CrossRef] [PubMed]

14.

G. Persichetti, G. Testa, and R. Bernini, “Optofluidic jet waveguide for laser-induced fluorescence spectroscopy,” Opt. Lett. 37(24), 5115–5117 (2012). [CrossRef] [PubMed]

15.

B. Richerzhagen, “Chip singulation process with a water-jet guided laser,” Solid State Technol. 44, 25–28 (2001).

16.

S. Folestad, L. Johnson, B. Josefsson, and B. Galle, “Laser-induced fluorescence detection for conventional and microcolumn liquid chromatography,” Anal. Chem. 54(6), 925–929 (1982). [CrossRef]

17.

J. W. S. Rayleigh, “On the instability of jets,” Proc. Lond. Math. Soc. 10(1), 4–13 (1878). [CrossRef]

18.

D. Colladon, “On the reflections of a ray of light inside a parabolic liquid stream,” CR (East Lansing, Mich.) 15, 800–802 (1842).

19.

R. J. van de Nesse, N. H. Velthorst, U. A. Th. Brinkman, and C. Gooijer, “Laser-induced fluorescence detection of native-fluorescent analytes in column liquid chromatography, a critical evaluation,” J. Chromatogr. A 704(1), 1–25 (1995). [CrossRef]

20.

P. C. H. Li, Microfluidic Lab-on-a-Chip for Chemical and Biological Analysis and Discovery (Taylor and Francis/CRC Press 2006), Chap. 7.

21.

K. M. Awati and T. Howes, “Stationary waves on cylindrical fluid jets,” Am. J. Phys. 64(6), 808–811 (1996).

22.

Y. Zhao, M. Jenkins, P. Measor, K. Leake, S. Liu, H. Schmidt, and A. R. Hawkins, “Hollow waveguides with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films,” Appl. Phys. Lett. 98(9), 091104 (2011). [CrossRef] [PubMed]

23.

S. Rajendran, M. A. Jog, and R. M. Manglik, “Experimental investigation of liquid jet breakup at low Weber number” in ILASS Americas,24th Annual Conference on Liquid Atomization and Spray Systems, (San Antonio, TX, 2012), pp. 1–6.

24.

J. Inczedy, T. Lengyel, and A. M. Ure, Compendium of analytical nomenclature. The orange book, 3rd edn., (Blackwell, Oxford 1998).

25.

L. V. Belovolova, M. V. Glushkov, E. A. Vinogradov, V. A. Babintsev, and V. I. Golovanov, “Ultraviolet fluorescence of water and highly diluted aqueous media,” Phys. Wave Phenom. 17(1), 21–31 (2009). [CrossRef]

26.

J. L. Shennan, “Hydrocarbons as substrates in industrial fermentation,” in Petroleum Microbiology R.M. Atlas, ed. (Macmillan Publishing Company, 1984).

27.

N. Billinton and A. W. Knight, “Seeing the wood through the trees: A review of techniques for distinguishing green fluorescent protein from endogenous autofluorescence,” Anal. Biochem. 291(2), 175–197 (2001). [CrossRef] [PubMed]

28.

E. T. Arakawa, N. V. Lavrik, and P. G. Datskos, “Detection of anthrax simulants with microcalorimetric spectroscopy: Bacillus subtilis and Bacillus cereus spores,” Appl. Opt. 42(10), 1757–1762 (2003). [CrossRef] [PubMed]

29.

A. B. Herzog, S. D. McLennan, A. K. Pandey, C. P. Gerba, C. N. Haas, J. B. Rose, and S. A. Hashsham, “Implications of limits of detection of various methods for Bacillus anthracis in computing risks to human health,” Appl. Environ. Microbiol. 75(19), 6331–6339 (2009). [CrossRef] [PubMed]

30.

R. Meidinger, R. W. St. Germain, V. Dohotariu, and G. D. Gillispie, Field Screening Methods for Hazardous Wastes and Toxic Chemicals (Air & Waste Management Association, 1993), Chap. Fluorescence of Aromatic Hydrocarbons in Aqueous Solutions.

31.

J. Sinfield, H. Hemond, J. Germaine, B. Johnson, and J. Bloch, “Contaminant detection, identification, and quantification using a microchip laser fluorescence sensor,” J. Environ. Eng. 133(3), 346–351 (2007). [CrossRef]

32.

U.S. Environmental Protection Agency, 2012Edition of the Drinking Water Standards and Health Advisories, EPA 822-S-12–001, http://water.epa.gov/action/advisories/drinking/upload/dwstandards2012.pdf.

OCIS Codes
(230.7370) Optical devices : Waveguides
(300.2530) Spectroscopy : Fluorescence, laser-induced
(300.6540) Spectroscopy : Spectroscopy, ultraviolet

ToC Category:
Spectroscopy

History
Original Manuscript: July 11, 2013
Revised Manuscript: August 30, 2013
Manuscript Accepted: August 30, 2013
Published: October 3, 2013

Citation
Gianluca Persichetti, Genni Gesta, and Romeo Bernini, "High sensitivity UV fluorescence spectroscopy based on an optofluidic jet waveguide," Opt. Express 21, 24219-24230 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-20-24219


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. W. E. Moerner and D. P. Fromm, “Methods of single-molecule fluorescence spectroscopy and microscopy,” Rev. Sci. Instrum.74(8), 3597–3619 (2003). [CrossRef]
  2. R. K. Henderson, A. Baker, K. R. Murphy, A. Hambly, R. M. Stuetz, and S. J. Khan, “Fluorescence as a potential monitoring tool for recycled water systems: A review,” Water Res.43(4), 863–881 (2009). [CrossRef] [PubMed]
  3. P. Karlitschek, F. Lewitzka, U. Bünting, M. Niederkrüger, and G. Marowsky, “Detection of aromatic pollutants in the environment by using UV-laser-induced fluorescence,” Appl. Phys. B67(4), 497–504 (1998). [CrossRef]
  4. D. Patra, “Applications and new developments in fluorescence spectroscopic techniques for the analysis of polycyclic aromatic hydrocarbons,” Appl. Spectrosc. Rev.38(2), 155–185 (2003). [CrossRef]
  5. P. J. Hargis, T. J. Sobering, G. C. Tisone, J. S. Wagner, S. A. Young, and R. J. Radloff, “Ultraviolet fluorescence identification of protein, DNA, and bacteria,” Proc. SPIE2366, 147–153 (1995). [CrossRef]
  6. L. Leblanc and E. Dufour, “Monitoring the identity of bacteria using their intrinsic fluorescence,” FEMS Microbiol. Lett.211(2), 147–153 (2002). [CrossRef] [PubMed]
  7. B. Kuswandi, J. Nuriman, J. Huskens, and W. Verboom, “Optical sensing systems for microfluidic devices: a review,” Anal. Chim. Acta601(2), 141–155 (2007). [CrossRef] [PubMed]
  8. C. Vannahme, S. Klinkhammer, U. Lemmer, and T. Mappes, “Plastic lab-on-a-chip for fluorescence excitation with integrated organic semiconductor lasers,” Opt. Express19(9), 8179–8186 (2011). [CrossRef] [PubMed]
  9. W. P. Risk, H. C. Kim, R. D. Miller, H. Temkin, and S. Gangopadhyay, “Optical waveguides with an aqueous core and a low-index nanoporous cladding,” Opt. Express12(26), 6446–6455 (2004). [CrossRef] [PubMed]
  10. A. Chen, M. M. Eberle, E. J. Lunt, S. Liu, K. Leake, M. I. Rudenko, A. R. Hawkins, and H. Schmidt, “Dual-color fluorescence cross-correlation spectroscopy on a planar optofluidic chip,” Lab Chip11(8), 1502–1506 (2011). [CrossRef] [PubMed]
  11. S. Smolka, M. Barth, and O. Benson, “Highly efficient fluorescence sensing with hollow core photonic crystal fibers,” Opt. Express15(20), 12783–12791 (2007). [CrossRef] [PubMed]
  12. A. E. Vasdekis and G. P. J. Laporte, “Enhancing single molecule imaging in optofluidics and microfluidics,” Int. J. Mol. Sci.12(12), 5135–5156 (2011). [CrossRef] [PubMed]
  13. J. Wu, G. Zheng, and L. M. Lee, “Optical imaging techniques in microfluidics and their applications,” Lab Chip12(19), 3566–3575 (2012). [CrossRef] [PubMed]
  14. G. Persichetti, G. Testa, and R. Bernini, “Optofluidic jet waveguide for laser-induced fluorescence spectroscopy,” Opt. Lett.37(24), 5115–5117 (2012). [CrossRef] [PubMed]
  15. B. Richerzhagen, “Chip singulation process with a water-jet guided laser,” Solid State Technol.44, 25–28 (2001).
  16. S. Folestad, L. Johnson, B. Josefsson, and B. Galle, “Laser-induced fluorescence detection for conventional and microcolumn liquid chromatography,” Anal. Chem.54(6), 925–929 (1982). [CrossRef]
  17. J. W. S. Rayleigh, “On the instability of jets,” Proc. Lond. Math. Soc.10(1), 4–13 (1878). [CrossRef]
  18. D. Colladon, “On the reflections of a ray of light inside a parabolic liquid stream,” CR (East Lansing, Mich.)15, 800–802 (1842).
  19. R. J. van de Nesse, N. H. Velthorst, U. A. Th. Brinkman, and C. Gooijer, “Laser-induced fluorescence detection of native-fluorescent analytes in column liquid chromatography, a critical evaluation,” J. Chromatogr. A704(1), 1–25 (1995). [CrossRef]
  20. P. C. H. Li, Microfluidic Lab-on-a-Chip for Chemical and Biological Analysis and Discovery (Taylor and Francis/CRC Press 2006), Chap. 7.
  21. K. M. Awati and T. Howes, “Stationary waves on cylindrical fluid jets,” Am. J. Phys.64(6), 808–811 (1996).
  22. Y. Zhao, M. Jenkins, P. Measor, K. Leake, S. Liu, H. Schmidt, and A. R. Hawkins, “Hollow waveguides with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films,” Appl. Phys. Lett.98(9), 091104 (2011). [CrossRef] [PubMed]
  23. S. Rajendran, M. A. Jog, and R. M. Manglik, “Experimental investigation of liquid jet breakup at low Weber number” in ILASS Americas,24th Annual Conference on Liquid Atomization and Spray Systems, (San Antonio, TX, 2012), pp. 1–6.
  24. J. Inczedy, T. Lengyel, and A. M. Ure, Compendium of analytical nomenclature. The orange book, 3rd edn., (Blackwell, Oxford 1998).
  25. L. V. Belovolova, M. V. Glushkov, E. A. Vinogradov, V. A. Babintsev, and V. I. Golovanov, “Ultraviolet fluorescence of water and highly diluted aqueous media,” Phys. Wave Phenom.17(1), 21–31 (2009). [CrossRef]
  26. J. L. Shennan, “Hydrocarbons as substrates in industrial fermentation,” in Petroleum Microbiology R.M. Atlas, ed. (Macmillan Publishing Company, 1984).
  27. N. Billinton and A. W. Knight, “Seeing the wood through the trees: A review of techniques for distinguishing green fluorescent protein from endogenous autofluorescence,” Anal. Biochem.291(2), 175–197 (2001). [CrossRef] [PubMed]
  28. E. T. Arakawa, N. V. Lavrik, and P. G. Datskos, “Detection of anthrax simulants with microcalorimetric spectroscopy: Bacillus subtilis and Bacillus cereus spores,” Appl. Opt.42(10), 1757–1762 (2003). [CrossRef] [PubMed]
  29. A. B. Herzog, S. D. McLennan, A. K. Pandey, C. P. Gerba, C. N. Haas, J. B. Rose, and S. A. Hashsham, “Implications of limits of detection of various methods for Bacillus anthracis in computing risks to human health,” Appl. Environ. Microbiol.75(19), 6331–6339 (2009). [CrossRef] [PubMed]
  30. R. Meidinger, R. W. St. Germain, V. Dohotariu, and G. D. Gillispie, Field Screening Methods for Hazardous Wastes and Toxic Chemicals (Air & Waste Management Association, 1993), Chap. Fluorescence of Aromatic Hydrocarbons in Aqueous Solutions.
  31. J. Sinfield, H. Hemond, J. Germaine, B. Johnson, and J. Bloch, “Contaminant detection, identification, and quantification using a microchip laser fluorescence sensor,” J. Environ. Eng.133(3), 346–351 (2007). [CrossRef]
  32. U.S. Environmental Protection Agency, 2012Edition of the Drinking Water Standards and Health Advisories, EPA 822-S-12–001, http://water.epa.gov/action/advisories/drinking/upload/dwstandards2012.pdf .

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited