Super-sensitivity in label-free protein sensing using a nanoslot nanolaser

doi:10.1364/OE.19.017683

Super-sensitivity in label-free protein sensing using a nanoslot nanolaser

Shota Kita, Shoji Hachuda, Shota Otsuka, Tatsuro Endo, Yasunori Imai, Yoshiaki Nishijima, Hiroaki Misawa, and Toshihiko Baba »View Author Affiliations

Optics Express, Vol. 19, Issue 18, pp. 17683-17690 (2011)
http://dx.doi.org/10.1364/OE.19.017683

View Full Text Article

Acrobat PDF (2558 KB)

Journal Search
Article Lookup

Article Tools

Citations

Alert me when this article is cited
Export Citation/Save

Full Text
Article Info
References (33)
Cited By
Figures (5)
Metrics

Abstract

Microphotonic sensors have been actively studied with increasing demands for label-free biosensing in medical diagnoses and life sciences. For high-throughput and low-cost sensing, a high sensitivity is crucial for eliminating the pre-concentration process, while a simple setup of sensors is also desirable. This paper demonstrates a super-sensitivity for protein, which satisfies these requirements. The key device is a photonic crystal nanolaser, in particular with a nanoslot. Even using a simple setup, the nanolaser achieves an extraordinary-low detection limit for BSA protein, i.e. 255 fM on an average, which cannot be explained by its bulk index sensitivity. The specific adsorption of the protein is observed only around the nanoslot with strong laser intensity. This suggests that the super-sensitivity arises from the effective trapping of protein in the nanoslot.

1. Introduction

In the field of biosensing, the detection of protein is becoming important for tumor markers, allergy testing, cytoscopy and proteomics [1

S. Ray, H. Chandra, and S. Srivastava, “Nanotechniques in proteomics: current status, promises and challenges,” Biosens. Bioelectron. 25(11), 2389–2401 (2010). [CrossRef] [PubMed]

X. D. Fan, I. M. White, S. I. Shopova, H. Y. Zhu, J. D. Suter, and Y. Z. Sun, “Sensitive optical biosensors for unlabeled targets: a review,” Anal. Chim. Acta 620(1-2), 8–26 (2008). [CrossRef] [PubMed]

]. Current methods, however, require complicated screening and concentration processes prior to sensing. Direct detection is more desirable for high-throughput analyses, but high selectivity and high sensitivity giving a low detection limit (DL) (pM order for tumor markers [3

P. R. Srinivas, M. Verma, Y. M. Zhao, and S. Srivastava, “Proteomics for cancer biomarker discovery,” Clin. Chem. 48(8), 1160–1169 (2002). [PubMed]

]) are required. The selectivity is mainly attributed to antigen-antibody reactions and surface chemistry, while the sensitivity is attributed to the performance of sensors as transducers. The sensor chip and the overall system must be simple for cost reduction and disposable use, and the chip should be small enough to integrate with advanced inspection kits such as μ-TAS.

Now, we focus on the sensitivity of sensors as transducers. Fluorescent labels, which achieve a low DL of pM order [4

D. A. Lashkari, J. L. DeRisi, J. H. McCusker, A. F. Namath, C. Gentile, S. Y. Hwang, P. O. Brown, and R. W. Davis, “Yeast microarrays for genome wide parallel genetic and gene expression analysis,” Proc. Natl. Acad. Sci. U.S.A. 94(24), 13057–13062 (1997). [CrossRef] [PubMed]

B. Schweitzer and S. F. Kingsmore, “Measuring proteins on microarrays,” Curr. Opin. Biotechnol. 13(1), 14–19 (2002). [CrossRef] [PubMed]

], are widely used as transducers in biosensing. However, they are suspected to denature the targets and their functionalization complicates the overall process. Therefore, label-free methods using surface plasmon resonance (SPR) [6

J. Homola, S. S. Yee, and G. Gauglitz, “Surface plasmon resonance sensors: review,” Sens. Actuators B Chem. 54(1-2), 3–15 (1999). [CrossRef]

] and passive optical cavities [7

K. De Vos, I. Bartolozzi, E. Schacht, P. Bienstman, and R. Baets, “Silicon-on-Insulator microring resonator for sensitive and label-free biosensing,” Opt. Express 15(12), 7610–7615 (2007). [CrossRef] [PubMed]

–9

M. R. Lee and P. M. Fauchet, “Two-dimensional silicon photonic crystal based biosensing platform for protein detection,” Opt. Express 15(8), 4530–4535 (2007). [CrossRef] [PubMed]

] have been studied as alternatives. They detect the adsorption of bio-molecules through a resonant wavelength shift Δλ_s (or resonant angle). In general, however, they have issues such as large size, low sensitivity, wide resonant spectrum (linewidth Δλ_w), and/or complicated setup. Being proportional to Δλ_w/Δλ_s, DL has been limited to nM regime in most cases; a lower regime is achieved only by using an ultrahigh Q cavity with complicated equipment [8

A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science 317(5839), 783–787 (2007). [CrossRef] [PubMed]

], which may not be low-cost or disposable.

Recently, nanolasers have also been studied for sensing [10

M. Lončar, A. Scherer, and Y. M. Qiu, “Photonic crystal laser sources for chemical detection,” Appl. Phys. Lett. 82(26), 4648–4650 (2003). [CrossRef]

–16

T. W. Lu, P. T. Lin, K.-U. Sio, and P.-T. Lee, “Optical sensing of square lattice photonic crystal point-shifted nanocavity for protein adsorption detection,” Appl. Phys. Lett. 96(21), 213702 (2010). [CrossRef]

]. They are photopumped and the emission is detected through the same free space optics, hence they operate remotely without the need for any electrical contacts. Cost reduction, disposable use and integration are possible when the nanolaser as a sensor chip is isolated from other equipment. A small size and low DL can be achieved simultaneously, because Δλ_w under lasing is reduced independently of the Q factor when the spectral broadening due to thermal chirping [11

S. Kita, K. Nozaki, S. Hachuda, H. Watanabe, Y. Saito, S. Otsuka, T. Nakada, Y. Arita, and T. Baba, “Photonic crystal point-shift nanolaser with and without nanoslots—design, fabrication, lasing and sensing characteristics,” IEEE J. Sel. Top. Quantum Electron. (to be published).

] is suppressed. As a device specifically suitable for this purpose, we have reported the nanoslot (NS) photonic crystal nanolaser [12

S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett. 97(16), 161108 (2010). [CrossRef]

], as shown in Fig. 1 . In high-index-contrast waveguides and cavities, the modal electric field is confined strongly in the NS [17

J. T. Robinson, C. Manolatou, L. Chen, and M. Lipson, “Ultrasmall mode volumes in dielectric optical microcavities,” Phys. Rev. Lett. 95(14), 143901 (2005). [CrossRef] [PubMed]

], resulting in enhanced light-matter interaction and high sensitivity in liquids [12

S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett. 97(16), 161108 (2010). [CrossRef]

,18

A. Di Falco, L. O'Faolain, and T. F. Krauss, “Chemical sensing in slotted photonic crystal heterostructure cavities,” Appl. Phys. Lett. 94(6), 063503 (2009). [CrossRef]

]. Furthermore in water, our NS nanolaser has low thermal chirping and is particularly effective for a narrow Δλ_w of 18 pm with a high sensitivity of 410 nm/RIU, giving a liquid index resolution of 4.5 × 10⁻⁵ [12

S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett. 97(16), 161108 (2010). [CrossRef]

Fig. 1 NS nanolaser. (a) Schematic of whole structure with bio-molecules adsorbed, and modal energy distribution calculated by 3D finite-difference time-domain (FDTD) method. (b) Magnified cross-section of NS.

In this paper, we discuss protein sensing using this NS nanolaser and show that the advantage of the NS is not limited to the narrow spectrum. In this experiment, it exhibits a super-sensitivity giving a remarkably low DL. It is confirmed to originate from the accelerated adsorption of the protein at the NS, which may be occurring due to optical trapping. In the following, we briefly describe the device structure, fabrication, and the procedure of sensing a standard protein—bovine serum albumin (BSA). We then show the details of the sensing characteristics, particularly focusing on the unique behaviors in the regime of ultra-low BSA concentration. We present simple theoretical analyses and discuss the advantage of this device compared to others.

2. Device structure and protein adsorption process

As illustrated in Fig. 1, two airholes in a triangular-lattice air-bridge photonic crystal slab are shifted outwards (H0 structure [11

,13

S. Kita, K. Nozaki, and T. Baba, “Refractive index sensing utilizing a cw photonic crystal nanolaser and its array configuration,” Opt. Express 16(11), 8174–8180 (2008). [CrossRef] [PubMed]

,19

K. Nozaki, S. Kita, and T. Baba, “Room temperature continuous wave operation and controlled spontaneous emission in ultrasmall photonic crystal nanolaser,” Opt. Express 15(12), 7506–7514 (2007). [CrossRef] [PubMed]

]), and a NS with width w _NS is perforated. The laser mode is localized inside and around the NS. The laser wavelength shifts with the surrounding index n. The detailed device structure and the sensitivity against liquids, Δλ_s/Δn, have been reported in [12

S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett. 97(16), 161108 (2010). [CrossRef]

]. Devices with w _NS = 30−70 nm are fabricated into commercial GaInAsP/InP quantum-well wafer by using e-beam lithography, HI inductively-coupled plasma etching and HCl wet etching. Since the footprint of a single device is only ~10 μm square, high-throughput fabrication is possible even using e-beam lithography. The device is operated by pulsed photopumping at 980 nm (duty-ratio of 200, spot diameter of 20 μm) to avoid the excess heating and the subsequent laser emission is detected using a fluorescence microscope setup. The device does not show any degradation even after operating for 8 hours in water. Since the single sensing was completed within 1 minute in this experiment, the device does not deteriorate at all after hundreds of measurements.

Figure 2(a) shows the procedure of BSA adsorption. First, we functionalized the device with a hydroxyl group with 9% HCl / deionized water at 3°C, then with an amino group with 10% N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (APTES) and an aldehyde group with 2.5% glutaraldehyde (GA) at 20°C. We used BSA (molecular weight = 68 kDa) [20

C. Silva, F. Sousa, G. G. Bitz, and A. Cavaco-Paulo, “Chemical modifications on proteins using glutaraldehyde,” Food Technol. Biotechnol. 42, 51–56 (2004).

] as a target protein which nonspecifically cross-links with GA. Figure 2(b) shows scanning electron micrograph (SEM) and atomic force micrograph (AFM) around the NS after soaking in high-concentration BSA aqueous solution of 10 μM for more than 30 minutes. More than 10-nm roughness is observed on the surface and in the NS, indicating the BSA adsorption, which was not observed before the process. Since BSA is known to have an elliptical shape and a molecular size larger than ~3 nm × 8 nm [21

C. Pacholski, M. Sartor, M. J. Sailor, F. Cunin, and G. M. Miskelly, “Biosensing using porous silicon double-layer interferometers: reflective interferometric Fourier transform spectroscopy,” J. Am. Chem. Soc. 127(33), 11636–11645 (2005). [CrossRef] [PubMed]

], the larger roughness observed suggests that the high-concentration BSA molecules agglutinate due to hydrophobic interaction and/or cross-linking through GA.

Fig. 2 Adsorption of BSA on device surface. (a) Schematic procedure. (b) Observation after adsorption process.

3. Observation of super-sensitivity

Figure 3(a) shows laser spectra for devices in water before and after the BSA adsorption. Here, the BSA concentration was 10 μM so that the device surface is covered with BSA almost completely. The clear redshift of the spectrum appears for both devices with and without the NS. Without the NS, the spectra are broadened by thermal chirping (Δλ_w > 600 pm). With the NS, the spectra are markedly narrowed due to athermalization [12

S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett. 97(16), 161108 (2010). [CrossRef]

] (Δλ_w < 30 pm), and the resolution is drastically improved. Figure 3(b) summarizes the dependence of Δλ_s on the NS width. The data scattering does not depend on the NS width. Therefore, it is thought to be due to the nonuniform adsorption of BSA between devices. The average Δλ_s with and without the NS are 4.4 and 2.2 nm, respectively. We theoretically estimated the overlap of the laser mode with the BSA film of a constant thickness using finite-difference time-domain (FDTD) simulation (see Supplements). It predicted a 1.2-fold enhancement of Δλ_s by the localized field in the NS and could not explain the 2-fold enhancement in Fig. 3(b). These results suggest that the adsorption is accelerated by the NS and the excess adsorption occurs nonuniformly around the NS.

Fig. 3 Biosensing characteristics. (a) Laser spectral shift before and after BSA adsorption. (b) Slot width dependence of wavelength shift. Dashed lines denote averages.

The accelerated adsorption is also suggested in the wide range of BSA concentrations C. Figure 4(a) shows spectral shifts for different C. The large shift in the high-concentration regime of ~10 nM, Shift_H, is observed for both with and without the NS. Shift_H is not saturated even in the high concentration regime of over 100 μM. This might be due to the physisorption, aggregation and phase transition [22

M. Noto, D. Keng, I. Teraoka, and S. Arnold, “Detection of protein orientation on the silica microsphere surface using transverse electric/transverse magnetic whispering gallery modes,” Biophys. J. 92(12), 4466–4472 (2007). [CrossRef] [PubMed]

] at particularly high concentrations (this could be a reason of the data scattering in Fig. 3(b)). On the other hand, the shift in the low concentration regime, Shift_L, is observed clearly only with the NS. This was observed repeatedly for all devices in different fabrication lots, but the concentration, at which Shift_L started, was distributed widely from <100 fM to >100 pM for different devices. We can consider that Shift_H arises from the adsorption over all other surfaces, while Shift_L from the adsorption inside the NS (see Supplements), and that the different concentration for Shift_L is due to the nonuniform adsorption as well as different NS width. Provided that each adsorption process occurs independently, Δλ_s is expressed as the following linear summation of three different Langmuir adsorption isotherms [23

H. J. Butt, K. Graf, and M. Kappl, Physics and Chemistry of Interfaces (Wiley-VCH, 2003). p. 195.

Fig. 4 Dependence on BSA concentration. (a) Laser spectra for different concentrations. (b) Wavelength shift with concentration. Circular plots show experimental data averaged over many devices with w _NS = 30 – 60 nm. Fitting curves are obtained from Eq. (1). Error bars for devices without NS denote temporal fluctuations due to the broadened spectrum. For NS devices, temporal fluctuations are negligible.

Δ λ_{s} = \frac{Δ λ_{max1} K_{A 1} C}{1 + K_{A 1} C} + \frac{Δ λ_{max2} K_{A 2} C}{1 + K_{A 2} C} + \frac{Δ λ_{max3} K_{A 3} C}{1 + K_{A 3} C}

(1)

where K _A1 and K _A2 are the affinity constants of the chemisorption inside and outside of the NS, respectively, and K _A3 is that of the physisorption. The latter two do not change in the presence of the NS. Δλ_maxi (i = 1, 2, 3) is the maximum shift when each adsorption is saturated. The circular plots in Fig. 4(b) shows Δλ_s averaged for many devices at different C. Error bars for the devices without the NS denote the temporal fluctuation in the spectral shift due to the broadened spectrum. For the devices with the NS, the temporal fluctuation is negligible. The solid line of Eq. (1) fit well with the experimental plots, when parameters in Table 1 are assumed. Here, K _A2 = 1.5 × 10⁷ M⁻¹ is a standard value for BSA [20

C. Silva, F. Sousa, G. G. Bitz, and A. Cavaco-Paulo, “Chemical modifications on proteins using glutaraldehyde,” Food Technol. Biotechnol. 42, 51–56 (2004).

]. On the other hand, K _A1 is more than four orders of magnitude larger than K _A2. This means that huge enhancement in BSA adsorption, which enhances the effective sensitivity, occurs at the NS. The DL is equivalent to C at Δλ_s = Δλ_w, and is given by

Table 1 Fitting parameters and DL for solid lines in Fig. 4(b)

	Affinity constant [M⁻¹]			Maximum shift [nm]			FWHM [nm] Δλ_w	DL
	K _A1	K _A2	K _A3	Δλ_max1	Δλ_max2	Δλ_max3	FWHM [nm] Δλ_w	DL
w/o NS	4.0 × 10¹⁰	1.5 × 10⁷	1.5 × 10⁵	0.2	1.7	1.0	0.60	38 nM (= 2.6 ug/ml)
w/ NS	2.5 × 10¹¹	1.5 × 10⁷	1.5 × 10⁵	0.5	2.2	1.9	0.03	255 fM (= 17 pg/ml)

DL = K_{Ai}^{- 1} (\frac{Δ λ_{w}}{Δ λ_{maxi} - Δ λ_{w}})

(2)

DLs obtained by substituting the parameters into Eq. (2) are also presented in Table 1. The DL for the averaged plots without the NS is calculated from K _A2 and Δλ_max2 to be 33 nM ( = 2.6 μg/ml, considering the molecular weight of BSA). The DL for those with the NS, calculated from K _A1 and Δλ_max1, is drastically improved to be 255 fM ( = 17 pg/ml). For the best NS device, the saturation in Δλ_s occurred at less than 1 pM, indicating that the lowest DL is less than 10 fM.

4. Possibility of trapping effect

Figure 5(a) shows the SEM picture at the NS after the measurement in the low-concentration regime (C < 1 pM). The specific adsorption is observed clearly under strong pumping (irradiation power at pulse peak P _irr = 15 mW), and not under weak pumping (P _irr = 6 mW). Figure 5(b) compares spectral shifts between three different conditions for the same C. Without the NS and under the strong pumping, a significant shift is not observed. With the NS, the shift increased from 0–0.1 to 0.5–0.8 nm when the pump power is switched from weak to strong. These results show clearly that the adsorption of BSA is accelerated by the specific trapping at the NS [24

A. H. J. Yang, S. D. Moore, B. S. Schmidt, M. Klug, M. Lipson, and D. Erickson, “Optical manipulation of nanoparticles and biomolecules in sub-wavelength slot waveguides,” Nature 457(7225), 71–75 (2009). [CrossRef] [PubMed]

], and it consistently explain the large enhancement of Δλ_s in Fig. 3(b) and the ultralow DL in Fig. 4(b).

Fig. 5 Dependence on pump power in the low-concentration regime (C = 1 pM). (a) SEM image around the NS after the measurement. (b) Spectral shift for several devices.

The trapping potential U _trap is estimated directly from K _Ai in Table 1 using the following equation [25

K. Shigemori, S. Nishizawa, T. Yokobori, T. Shioya, and N. Teramae, “Selective binding of very hydrophilic H2PO4- anion by a hydrogen-bonding receptor adsorbed at the 1,2-dichloroethane-water interface,” N. J. Chem. 26(9), 1102–1104 (2002). [CrossRef]

U_{trap} = k_{B} T \ln (K_{A 1} / K_{A 2})

(3)

where k _B T is the thermal energy. This equation and results in Table 1 gives U _trap = 9.7k _B T. Possible mechanisms of the trapping include the optical gradient force from the localized laser mode and/or from pump light, and also from the convection of water and/or thermal gradient force due to heating [26

R. Piazza, “‘Thermal forces’: colloids in temperature gradients,” J. Phys. Condens. Matter 16(38), S4195–S4211 (2004). [CrossRef]

]. For example, let us apply the expression for the optical gradient force [27

D. Erickson, X. Serey, Y. F. Chen, and S. Mandal, “Nanomanipulation using near field photonics,” Lab Chip 11(6), 995–1009 (2011). [CrossRef] [PubMed]

] to the laser mode. Then,

U_{trap} = \frac{D^{3}}{16} \cdot \frac{{(n_{p} / n_{w})}^{2} - 1}{{(n_{p} / n_{w})}^{2} + 2} \cdot \frac{ξ Q P}{ω V_{m}}

(4)

where D is the diameter of the protein when it is approximated as a sphere, n _p and n _w are the indices of the protein and water, respectively, ξ is the enhancement ratio of the modal energy in the NS to the average value, P is the radiated laser mode power, and V _m is the modal volume in water. The highest Q in the ideal cavity is calculated to be 15,000–7,000 for w _NS = 20–40 nm, respectively, also leading to V _m = 0.011–0.018 μm³ and ξ = 74–46. Assuming n _p = 1.5, n _w = 1.321, and D = 10 nm, the trapping threshold P satisfying U _trap > k _B T at T = 300 K becomes 10–59 μW. On the other hand, P in the experiment is roughly estimated to be 0.01P _irr = 150 μW under the strong pumping, which ensures a reasonable U _trap = 15–2.5k _B T in comparison with that from Eq. (3). Thus this force is a possible trapping mechanism. Other mechanisms are also worth considering, because they could explain the continuous supply of dispersed BSA molecules to the NS.

5. Comparison with other label-free biosensors

Table 2 compares the performance of label-free biosensors including this work. Since targets are different between reports, standard values of K _A in literatures change from 10⁵–10¹¹ M⁻¹. In general, the detection becomes easier and DL is improved for larger K _A. Therefore, the performance should be evaluated from the product of DL and K _A. Let us define the figure-of-merit (FOM) factor as (DL × K _A)⁻¹ normalized by that for the SPR sensor [28

W. C. Law, K. T. Yong, A. Baev, R. Hu, and P. N. Prasad, “Nanoparticle enhanced surface plasmon resonance biosensing: application of gold nanorods,” Opt. Express 17(21), 19041–19046 (2009). [CrossRef] [PubMed]

]. The nanolaser achieves a FOM of 230. To date, FOMs higher than this value have been reported only for Au nanoparticles [29

D. S. Grubisha, R. J. Lipert, H. Y. Park, J. Driskell, and M. D. Porter, “Femtomolar detection of prostate-specific antigen: an immunoassay based on surface-enhanced Raman scattering and immunogold labels,” Anal. Chem. 75(21), 5936–5943 (2003). [CrossRef] [PubMed]

] and ultrahigh-Q micro-toroidal cavity [8

] although they have drawbacks such as unstable DL, large sensing area, and complicated I/O. Other passive cavities and interferometers do not meet the requirement for the low DL, and their optical I/O can be a large bottleneck in cost reduction. In comparison, the nanolaser satisfies the requirements of simple fabrication, easy sensing and excellent DL. By using nanolasers as sensor chips isolated from other equipment, the cost reduction and disposable use will be possible. In addition, further investigations and controlled trapping mechanisms will lead to a unique tool for the efficient manipulation and detection of targets in biosensing.

Performance of label-free biosensors

Device	Sample (K _A [M⁻¹])	DL [pg/ml]	FOM (DL × K _A)⁻¹	Sensing area [μm²]	Details	Ref.
SPR
SPR	IgG (~10⁹)	40	1	10⁴−10⁶	Simple, broad Δλ_w	[28 W. C. Law, K. T. Yong, A. Baev, R. Hu, and P. N. Prasad, “Nanoparticle enhanced surface plasmon resonance biosensing: application of gold nanorods,” Opt. Express 17(21), 19041–19046 (2009). [CrossRef] [PubMed] ]
CNT FET	IgG (~10⁹)	1	39	~6	Fast, fragile	[30 J. P. Kim, B. Y. Lee, S. Hong, and S. J. Sim, “Ultrasensitive carbon nanotube-based biosensors using antibody-binding fragments,” Anal. Biochem. 381(2), 193–198 (2008). [CrossRef] [PubMed] ]
Au nanoparticle	BSA (~10⁷)	4	1,000	<1	Nonuniformity	[29 D. S. Grubisha, R. J. Lipert, H. Y. Park, J. Driskell, and M. D. Porter, “Femtomolar detection of prostate-specific antigen: an immunoassay based on surface-enhanced Raman scattering and immunogold labels,” Anal. Chem. 75(21), 5936–5943 (2003). [CrossRef] [PubMed] ]
Si μ-ring	BSA (~10⁷)	10⁴	0.6	~60	Si CMOS compatible, narrow Δλ_w, fiber I/O	[7 K. De Vos, I. Bartolozzi, E. Schacht, P. Bienstman, and R. Baets, “Silicon-on-Insulator microring resonator for sensitive and label-free biosensing,” Opt. Express 15(12), 7610–7615 (2007). [CrossRef] [PubMed] ]
SiO₂ μ-toroidal	IL-2 (~10¹¹)	8 × 10⁻⁵	4,700	~6,000	Ultranarrow Δλ_w, taper fiber I/O	[8 A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science 317(5839), 783–787 (2007). [CrossRef] [PubMed] ]
Si wire MZI	IgG (~10⁹)	2,900	0.01	>20,000	Si CMOS compatible, fiber I/O	[31 A. Densmore, M. Vachon, D. X. Xu, S. Janz, R. Ma, Y. H. Li, G. Lopinski, A. Delâge, J. Lapointe, C. C. Luebbert, Q. Y. Liu, P. Cheben, and J. H. Schmid, “Silicon photonic wire biosensor array for multiplexed real-time and label-free molecular detection,” Opt. Lett. 34(23), 3598–3600 (2009). [CrossRef] [PubMed] ]
Si PC waveguide	BSA (~10⁵) (Physisorption)	10⁷	0.04	~100	Si CMOS compatible, fiber I/O	[32 N. Skivesen, A. Têtu, M. Kristensen, J. Kjems, L. H. Frandsen, and P. I. Borel, “Photonic-crystal waveguide biosensor,” Opt. Express 15(6), 3169–3176 (2007). [CrossRef] [PubMed] ]
Si PC nanocavity	Anti-biotin (~10⁷)	1,400	2.9	~3	Si CMOS compatible, narrow Δλ_w, fiber I/O	[33 S. Zlatanovic, L. W. Mirkarimi, M. M. Sigalas, M. A. Bynum, E. Chow, K. M. Robotti, G. W. Burr, S. Esener, and A. Grot, “Photonic crystal microcavity sensor for ultracompact monitoring of reaction kinetics and protein concentration,” Sens. Actuators B Chem. 141(1), 13–19 (2009). [CrossRef] ]
*NS nanolaser (This work)*	BSA (~10⁷)	17	230	<1	Simple, very narrow Δλ_w	[11 S. Kita, K. Nozaki, S. Hachuda, H. Watanabe, Y. Saito, S. Otsuka, T. Nakada, Y. Arita, and T. Baba, “Photonic crystal point-shift nanolaser with and without nanoslots—design, fabrication, lasing and sensing characteristics,” IEEE J. Sel. Top. Quantum Electron. (to be published). ], [12 S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett. 97(16), 161108 (2010). [CrossRef] ]

6. Supplements

We performed two FDTD calculations that help the understanding of the experimental results. The first one concerns the spectral shift with and without the NS, approximating the adsorbed BSA as a 20-nm thick film. Since the biosensing only targets the film, its index sensitivity Δλ_s/Δn _f decreases from the bulk index sensitivity Δλ_s/Δn _b. We calculated Δλ_s/Δn _f to be 96 and 80 nm/RIU with and without the NS, respectively, which are 29 and 23% of Δλ_s/Δn _b in [12

S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett. 97(16), 161108 (2010). [CrossRef]

]. The enhancement due to the NS is only 1.2 times. Even though the mode appears to be localized inside the NS in Fig. 1(a), its small intensity is also distributed widely outside, and this reflects the small enhancement. In any case, the super-sensitivity in the experiment cannot be explained by this enhancement.

The second one is the spectral shift for the local adsorption inside the NS. It was calculated to be 26–6% of the adsorption over the whole device surface when w _NS = 10–50 nm, respectively. This roughly corresponds to the experimental ratio Δλ_max1/Σ_iΔλ_maxi = 11%, and supports the discussion that Shift_L is due to the selective adsorption inside the NS.

References and links

1.	S. Ray, H. Chandra, and S. Srivastava, “Nanotechniques in proteomics: current status, promises and challenges,” Biosens. Bioelectron. 25(11), 2389–2401 (2010). [CrossRef] [PubMed]
2.	X. D. Fan, I. M. White, S. I. Shopova, H. Y. Zhu, J. D. Suter, and Y. Z. Sun, “Sensitive optical biosensors for unlabeled targets: a review,” Anal. Chim. Acta 620(1-2), 8–26 (2008). [CrossRef] [PubMed]
3.	P. R. Srinivas, M. Verma, Y. M. Zhao, and S. Srivastava, “Proteomics for cancer biomarker discovery,” Clin. Chem. 48(8), 1160–1169 (2002). [PubMed]
4.	D. A. Lashkari, J. L. DeRisi, J. H. McCusker, A. F. Namath, C. Gentile, S. Y. Hwang, P. O. Brown, and R. W. Davis, “Yeast microarrays for genome wide parallel genetic and gene expression analysis,” Proc. Natl. Acad. Sci. U.S.A. 94(24), 13057–13062 (1997). [CrossRef] [PubMed]
5.	B. Schweitzer and S. F. Kingsmore, “Measuring proteins on microarrays,” Curr. Opin. Biotechnol. 13(1), 14–19 (2002). [CrossRef] [PubMed]
6.	J. Homola, S. S. Yee, and G. Gauglitz, “Surface plasmon resonance sensors: review,” Sens. Actuators B Chem. 54(1-2), 3–15 (1999). [CrossRef]
7.	K. De Vos, I. Bartolozzi, E. Schacht, P. Bienstman, and R. Baets, “Silicon-on-Insulator microring resonator for sensitive and label-free biosensing,” Opt. Express 15(12), 7610–7615 (2007). [CrossRef] [PubMed]
8.	A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science 317(5839), 783–787 (2007). [CrossRef] [PubMed]
9.	M. R. Lee and P. M. Fauchet, “Two-dimensional silicon photonic crystal based biosensing platform for protein detection,” Opt. Express 15(8), 4530–4535 (2007). [CrossRef] [PubMed]
10.	M. Lončar, A. Scherer, and Y. M. Qiu, “Photonic crystal laser sources for chemical detection,” Appl. Phys. Lett. 82(26), 4648–4650 (2003). [CrossRef]
11.	S. Kita, K. Nozaki, S. Hachuda, H. Watanabe, Y. Saito, S. Otsuka, T. Nakada, Y. Arita, and T. Baba, “Photonic crystal point-shift nanolaser with and without nanoslots—design, fabrication, lasing and sensing characteristics,” IEEE J. Sel. Top. Quantum Electron. (to be published).
12.	S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett. 97(16), 161108 (2010). [CrossRef]
13.	S. Kita, K. Nozaki, and T. Baba, “Refractive index sensing utilizing a cw photonic crystal nanolaser and its array configuration,” Opt. Express 16(11), 8174–8180 (2008). [CrossRef] [PubMed]
14.	M. A. Dündar, E. C. I. Ryckebosch, R. Nötzel, F. Karouta, L. J. van Ijzendoorn, and R. W. van der Heijden, “Sensitivities of InGaAsP photonic crystal membrane nanocavities to hole refractive index,” Opt. Express 18(5), 4049–4056 (2010). [CrossRef] [PubMed]
15.	S. Kita, Y. Nishijima, H. Misawa and T. Baba, "Label-free biosensing utilizing ultrasmall photonic crystal nanolaser," in Integrated Photonics and Nanophotonics Research and Applications, OSA Technical Digest (CD) (Optical Society of America, 2009), paper IMB3.
16.	T. W. Lu, P. T. Lin, K.-U. Sio, and P.-T. Lee, “Optical sensing of square lattice photonic crystal point-shifted nanocavity for protein adsorption detection,” Appl. Phys. Lett. 96(21), 213702 (2010). [CrossRef]
17.	J. T. Robinson, C. Manolatou, L. Chen, and M. Lipson, “Ultrasmall mode volumes in dielectric optical microcavities,” Phys. Rev. Lett. 95(14), 143901 (2005). [CrossRef] [PubMed]
18.	A. Di Falco, L. O'Faolain, and T. F. Krauss, “Chemical sensing in slotted photonic crystal heterostructure cavities,” Appl. Phys. Lett. 94(6), 063503 (2009). [CrossRef]
19.	K. Nozaki, S. Kita, and T. Baba, “Room temperature continuous wave operation and controlled spontaneous emission in ultrasmall photonic crystal nanolaser,” Opt. Express 15(12), 7506–7514 (2007). [CrossRef] [PubMed]
20.	C. Silva, F. Sousa, G. G. Bitz, and A. Cavaco-Paulo, “Chemical modifications on proteins using glutaraldehyde,” Food Technol. Biotechnol. 42, 51–56 (2004).
21.	C. Pacholski, M. Sartor, M. J. Sailor, F. Cunin, and G. M. Miskelly, “Biosensing using porous silicon double-layer interferometers: reflective interferometric Fourier transform spectroscopy,” J. Am. Chem. Soc. 127(33), 11636–11645 (2005). [CrossRef] [PubMed]
22.	M. Noto, D. Keng, I. Teraoka, and S. Arnold, “Detection of protein orientation on the silica microsphere surface using transverse electric/transverse magnetic whispering gallery modes,” Biophys. J. 92(12), 4466–4472 (2007). [CrossRef] [PubMed]
23.	H. J. Butt, K. Graf, and M. Kappl, Physics and Chemistry of Interfaces (Wiley-VCH, 2003). p. 195.
24.	A. H. J. Yang, S. D. Moore, B. S. Schmidt, M. Klug, M. Lipson, and D. Erickson, “Optical manipulation of nanoparticles and biomolecules in sub-wavelength slot waveguides,” Nature 457(7225), 71–75 (2009). [CrossRef] [PubMed]
25.	K. Shigemori, S. Nishizawa, T. Yokobori, T. Shioya, and N. Teramae, “Selective binding of very hydrophilic H2PO4- anion by a hydrogen-bonding receptor adsorbed at the 1,2-dichloroethane-water interface,” N. J. Chem. 26(9), 1102–1104 (2002). [CrossRef]
26.	R. Piazza, “‘Thermal forces’: colloids in temperature gradients,” J. Phys. Condens. Matter 16(38), S4195–S4211 (2004). [CrossRef]
27.	D. Erickson, X. Serey, Y. F. Chen, and S. Mandal, “Nanomanipulation using near field photonics,” Lab Chip 11(6), 995–1009 (2011). [CrossRef] [PubMed]
28.	W. C. Law, K. T. Yong, A. Baev, R. Hu, and P. N. Prasad, “Nanoparticle enhanced surface plasmon resonance biosensing: application of gold nanorods,” Opt. Express 17(21), 19041–19046 (2009). [CrossRef] [PubMed]
29.	D. S. Grubisha, R. J. Lipert, H. Y. Park, J. Driskell, and M. D. Porter, “Femtomolar detection of prostate-specific antigen: an immunoassay based on surface-enhanced Raman scattering and immunogold labels,” Anal. Chem. 75(21), 5936–5943 (2003). [CrossRef] [PubMed]
30.	J. P. Kim, B. Y. Lee, S. Hong, and S. J. Sim, “Ultrasensitive carbon nanotube-based biosensors using antibody-binding fragments,” Anal. Biochem. 381(2), 193–198 (2008). [CrossRef] [PubMed]
31.	A. Densmore, M. Vachon, D. X. Xu, S. Janz, R. Ma, Y. H. Li, G. Lopinski, A. Delâge, J. Lapointe, C. C. Luebbert, Q. Y. Liu, P. Cheben, and J. H. Schmid, “Silicon photonic wire biosensor array for multiplexed real-time and label-free molecular detection,” Opt. Lett. 34(23), 3598–3600 (2009). [CrossRef] [PubMed]
32.	N. Skivesen, A. Têtu, M. Kristensen, J. Kjems, L. H. Frandsen, and P. I. Borel, “Photonic-crystal waveguide biosensor,” Opt. Express 15(6), 3169–3176 (2007). [CrossRef] [PubMed]
33.	S. Zlatanovic, L. W. Mirkarimi, M. M. Sigalas, M. A. Bynum, E. Chow, K. M. Robotti, G. W. Burr, S. Esener, and A. Grot, “Photonic crystal microcavity sensor for ultracompact monitoring of reaction kinetics and protein concentration,” Sens. Actuators B Chem. 141(1), 13–19 (2009). [CrossRef]

OCIS Codes
(280.1415) Remote sensing and sensors : Biological sensing and sensors
(140.3945) Lasers and laser optics : Microcavities
(230.5298) Optical devices : Photonic crystals

ToC Category:
Sensors

History
Original Manuscript: June 14, 2011
Revised Manuscript: July 25, 2011
Manuscript Accepted: August 13, 2011
Published: August 24, 2011

Virtual Issues
Vol. 6, Iss. 9 Virtual Journal for Biomedical Optics

Citation
Shota Kita, Shoji Hachuda, Shota Otsuka, Tatsuro Endo, Yasunori Imai, Yoshiaki Nishijima, Hiroaki Misawa, and Toshihiko Baba, "Super-sensitivity in label-free protein sensing using a nanoslot nanolaser," Opt. Express 19, 17683-17690 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-18-17683

Sort: Author | Year | Journal | Reset

References

S. Ray, H. Chandra, and S. Srivastava, “Nanotechniques in proteomics: current status, promises and challenges,” Biosens. Bioelectron.25(11), 2389–2401 (2010). [CrossRef] [PubMed]
X. D. Fan, I. M. White, S. I. Shopova, H. Y. Zhu, J. D. Suter, and Y. Z. Sun, “Sensitive optical biosensors for unlabeled targets: a review,” Anal. Chim. Acta620(1-2), 8–26 (2008). [CrossRef] [PubMed]
P. R. Srinivas, M. Verma, Y. M. Zhao, and S. Srivastava, “Proteomics for cancer biomarker discovery,” Clin. Chem.48(8), 1160–1169 (2002). [PubMed]
D. A. Lashkari, J. L. DeRisi, J. H. McCusker, A. F. Namath, C. Gentile, S. Y. Hwang, P. O. Brown, and R. W. Davis, “Yeast microarrays for genome wide parallel genetic and gene expression analysis,” Proc. Natl. Acad. Sci. U.S.A.94(24), 13057–13062 (1997). [CrossRef] [PubMed]
B. Schweitzer and S. F. Kingsmore, “Measuring proteins on microarrays,” Curr. Opin. Biotechnol.13(1), 14–19 (2002). [CrossRef] [PubMed]
J. Homola, S. S. Yee, and G. Gauglitz, “Surface plasmon resonance sensors: review,” Sens. Actuators B Chem.54(1-2), 3–15 (1999). [CrossRef]
K. De Vos, I. Bartolozzi, E. Schacht, P. Bienstman, and R. Baets, “Silicon-on-Insulator microring resonator for sensitive and label-free biosensing,” Opt. Express15(12), 7610–7615 (2007). [CrossRef] [PubMed]
A. M. Armani, R. P. Kulkarni, S. E. Fraser, R. C. Flagan, and K. J. Vahala, “Label-free, single-molecule detection with optical microcavities,” Science317(5839), 783–787 (2007). [CrossRef] [PubMed]
M. R. Lee and P. M. Fauchet, “Two-dimensional silicon photonic crystal based biosensing platform for protein detection,” Opt. Express15(8), 4530–4535 (2007). [CrossRef] [PubMed]
M. Lončar, A. Scherer, and Y. M. Qiu, “Photonic crystal laser sources for chemical detection,” Appl. Phys. Lett.82(26), 4648–4650 (2003). [CrossRef]
S. Kita, K. Nozaki, S. Hachuda, H. Watanabe, Y. Saito, S. Otsuka, T. Nakada, Y. Arita, and T. Baba, “Photonic crystal point-shift nanolaser with and without nanoslots—design, fabrication, lasing and sensing characteristics,” IEEE J. Sel. Top. Quantum Electron.(to be published).
S. Kita, S. Hachuda, K. Nozaki, and T. Baba, “Nanoslot laser,” Appl. Phys. Lett.97(16), 161108 (2010). [CrossRef]
S. Kita, K. Nozaki, and T. Baba, “Refractive index sensing utilizing a cw photonic crystal nanolaser and its array configuration,” Opt. Express16(11), 8174–8180 (2008). [CrossRef] [PubMed]
M. A. Dündar, E. C. I. Ryckebosch, R. Nötzel, F. Karouta, L. J. van Ijzendoorn, and R. W. van der Heijden, “Sensitivities of InGaAsP photonic crystal membrane nanocavities to hole refractive index,” Opt. Express18(5), 4049–4056 (2010). [CrossRef] [PubMed]
S. Kita, Y. Nishijima, H. Misawa and T. Baba, "Label-free biosensing utilizing ultrasmall photonic crystal nanolaser," in Integrated Photonics and Nanophotonics Research and Applications, OSA Technical Digest (CD) (Optical Society of America, 2009), paper IMB3.
T. W. Lu, P. T. Lin, K.-U. Sio, and P.-T. Lee, “Optical sensing of square lattice photonic crystal point-shifted nanocavity for protein adsorption detection,” Appl. Phys. Lett.96(21), 213702 (2010). [CrossRef]
J. T. Robinson, C. Manolatou, L. Chen, and M. Lipson, “Ultrasmall mode volumes in dielectric optical microcavities,” Phys. Rev. Lett.95(14), 143901 (2005). [CrossRef] [PubMed]
A. Di Falco, L. O'Faolain, and T. F. Krauss, “Chemical sensing in slotted photonic crystal heterostructure cavities,” Appl. Phys. Lett.94(6), 063503 (2009). [CrossRef]
K. Nozaki, S. Kita, and T. Baba, “Room temperature continuous wave operation and controlled spontaneous emission in ultrasmall photonic crystal nanolaser,” Opt. Express15(12), 7506–7514 (2007). [CrossRef] [PubMed]
C. Silva, F. Sousa, G. G. Bitz, and A. Cavaco-Paulo, “Chemical modifications on proteins using glutaraldehyde,” Food Technol. Biotechnol.42, 51–56 (2004).
C. Pacholski, M. Sartor, M. J. Sailor, F. Cunin, and G. M. Miskelly, “Biosensing using porous silicon double-layer interferometers: reflective interferometric Fourier transform spectroscopy,” J. Am. Chem. Soc.127(33), 11636–11645 (2005). [CrossRef] [PubMed]
M. Noto, D. Keng, I. Teraoka, and S. Arnold, “Detection of protein orientation on the silica microsphere surface using transverse electric/transverse magnetic whispering gallery modes,” Biophys. J.92(12), 4466–4472 (2007). [CrossRef] [PubMed]
H. J. Butt, K. Graf, and M. Kappl, Physics and Chemistry of Interfaces (Wiley-VCH, 2003). p. 195.
A. H. J. Yang, S. D. Moore, B. S. Schmidt, M. Klug, M. Lipson, and D. Erickson, “Optical manipulation of nanoparticles and biomolecules in sub-wavelength slot waveguides,” Nature457(7225), 71–75 (2009). [CrossRef] [PubMed]
K. Shigemori, S. Nishizawa, T. Yokobori, T. Shioya, and N. Teramae, “Selective binding of very hydrophilic H2PO4- anion by a hydrogen-bonding receptor adsorbed at the 1,2-dichloroethane-water interface,” N. J. Chem.26(9), 1102–1104 (2002). [CrossRef]
R. Piazza, “‘Thermal forces’: colloids in temperature gradients,” J. Phys. Condens. Matter16(38), S4195–S4211 (2004). [CrossRef]
D. Erickson, X. Serey, Y. F. Chen, and S. Mandal, “Nanomanipulation using near field photonics,” Lab Chip11(6), 995–1009 (2011). [CrossRef] [PubMed]
W. C. Law, K. T. Yong, A. Baev, R. Hu, and P. N. Prasad, “Nanoparticle enhanced surface plasmon resonance biosensing: application of gold nanorods,” Opt. Express17(21), 19041–19046 (2009). [CrossRef] [PubMed]
D. S. Grubisha, R. J. Lipert, H. Y. Park, J. Driskell, and M. D. Porter, “Femtomolar detection of prostate-specific antigen: an immunoassay based on surface-enhanced Raman scattering and immunogold labels,” Anal. Chem.75(21), 5936–5943 (2003). [CrossRef] [PubMed]
J. P. Kim, B. Y. Lee, S. Hong, and S. J. Sim, “Ultrasensitive carbon nanotube-based biosensors using antibody-binding fragments,” Anal. Biochem.381(2), 193–198 (2008). [CrossRef] [PubMed]
A. Densmore, M. Vachon, D. X. Xu, S. Janz, R. Ma, Y. H. Li, G. Lopinski, A. Delâge, J. Lapointe, C. C. Luebbert, Q. Y. Liu, P. Cheben, and J. H. Schmid, “Silicon photonic wire biosensor array for multiplexed real-time and label-free molecular detection,” Opt. Lett.34(23), 3598–3600 (2009). [CrossRef] [PubMed]
N. Skivesen, A. Têtu, M. Kristensen, J. Kjems, L. H. Frandsen, and P. I. Borel, “Photonic-crystal waveguide biosensor,” Opt. Express15(6), 3169–3176 (2007). [CrossRef] [PubMed]
S. Zlatanovic, L. W. Mirkarimi, M. M. Sigalas, M. A. Bynum, E. Chow, K. M. Robotti, G. W. Burr, S. Esener, and A. Grot, “Photonic crystal microcavity sensor for ultracompact monitoring of reaction kinetics and protein concentration,” Sens. Actuators B Chem.141(1), 13–19 (2009). [CrossRef]

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.

Click here to see a list of articles that cite this paper