Signal-to-noise ratio is a crucial issue in microarray fluorescence read-out. Several strategies are proposed for its improvement. First, light collection in conventional microarrays scanners is quite limited. It was recently shown that almost full collection can be achieved in an integrated lens-free biosensor, with labelled species hybridizing practically on the surface of a sensitive silicon detector [L. Martinelli et al. Appl. Phys. Lett. 91, 083901 (2007)]. However, even with such an improvement, the ultimate goal of real-time measurements during hybridization is challenging: the detector is dazzled by the large fluorescence of labelled species in the solution. In the present paper we show that this unwanted signal can effectively be reduced if the excitation light is confined in a waveguide. Moreover, the concentration of excitation light in a waveguide results in a huge signal gain. In our experiment we realized a structure consisting of a high index sol-gel waveguide deposited on a low-index substrate. The fluorescent molecules deposited on the surface of the waveguide were excited by the evanescent part of a wave travelling in the guide. The comparison with free-space excitation schemes confirms a huge gain (by several orders of magnitude) in favour of waveguide-based excitation. An optical guide deposited onto an integrated biosensor thus combines both advantages of ideal light collection and enhanced surface localized excitation without compromising the imaging properties. Modelling predicts a negligible penalty from spatial cross-talk in practical applications. We believe that such a system would bring microarrays to hitherto unattained sensitivities.
[1]
Gert Ludwig Duveneck,et al.
Planar waveguides for ultra-high sensitivity of the analysis of nucleic acids
,
2002
.
[2]
Wolfgang Budach,et al.
Planar Waveguides as High-Performance Sensing Platforms for Fluorescence-Based Multiplexed Oligonucleotide Hybridization Assays
,
1999
.
[3]
Arjang Hassibi,et al.
Modeling and simulation of luminescence detection platforms.
,
2004,
Biosensors & bioelectronics.
[4]
Albrecht Brandenburg,et al.
Modeling and experimental verification of the performance of TIRF-sensing systems for oligonucleotide microarrays based on bulk and integrated optical planar waveguides
,
2003
.
[5]
C. Weisbuch,et al.
Impact of planar microcavity effects on light extraction-Part I: basic concepts and analytical trends
,
1998
.
[6]
Henri Benisty,et al.
Sensor-integrated fluorescent microarray for ultrahigh sensitivity direct-imaging bioassays: Role of a high rejection of excitation light
,
2007
.
[7]
G. Sulz,et al.
Real-time detection of nucleic acid interactions by total internal reflection fluorescence.
,
2003,
Analytical chemistry.