Microbial culture continues to be the most common protocol for bacterial detection and identification in medicine and agronomics. Using this process may take days to identify a specific pathogen for most bacterial strains. Surface Plasmon Resonance (SPR) detection is an emerging alternative technology that can be used for the detection of bacteria using protein microarrays although typical limits of detection are in the range of 10³–10⁶ cfu mL⁻¹, which is not compatible with most Food Safety regulation requirements. In this work, we combine concomitant “on-chip” microbial culture with sensitive SPR detection of bacteria thus allowing rapid specific detection of bacteria pathogens – including Salmonella enterica serovar Enteritidis, Streptococcus pneumoniae and Escherichia coli O157:H7 – cultured on a protein microarray. This Culture–Capture–Measure (CCM) approach significantly decreases both the number of processing steps and the overall assay time for bacterial detection. Signal analysis of SPR responses allowed the fast and quantitative assessment of bacterial concentrations initially present in the sample as low as 2.8 ± 19.6 cfu per milliliter. Altogether, our results show how simple, easy-to-operate, fluidic-less and lo-tec microarrays can be used with unprocessed samples and yield – in a single assay – both qualitative and quantitative information regarding bacterial contamination.

Several optical surface sensing techniques, such as Surface Plasmon Resonance (SPR), work by imaging the base of a prism by one of its faces. However, such a fundamental optical concern has not been fully analyzed and understood so far, and spatial resolution remains a critical and controversial issue. In SPR, the propagation length L_x of the surface plasmon waves has been considered as the limiting factor. Here, we demonstrate that for unoptimized systems geometrical aberrations caused by the prism can be more limiting than the propagation length. By combining line-scan imaging mode with optimized prisms, we access the ultimate lateral resolution which is diffraction-limited by the object light diffusion. We describe several optimized configurations in water and discuss the trade-off between L_x and sensitivity. The improvement of resolution is confirmed by imaging micro-structured PDMS stamps and individual living eukaryote cells and bacteria on field-of-view from 0.1 to 20 mm².

We demonstrate the use of SPR imaging for the detection of site-specific binding of either B or T lymphocyte populations on an electrochemically-grafted antibody array.

Aptamers are selected DNA ligands that target biomolecules such as proteins. In recent years, they are showing an increasing interest as potential therapeutic agents or recognition elements in biosensor applications. In both cases, the need for characterizing the mating between the target and the aptamer either in solution or immobilized on a surface, is pressing. In this context, we have developed a kinetic biosensor made of micro-arrayed anti-thrombin aptamers to assess the kinetic parameters of this interaction. The binding of label-free thrombin on the biosensor was monitored in real-time by Surface Plasmon Resonance imaging. Remarkable performances were obtained for the quantification of thrombin without amplification (sub-nanomolar limit of detection and linear range of quantification to two orders of magnitude). The independent determinations of both the solution- and surface-phase affinities, respectively K_D^Sol and K_D^Surf, revealed distinct values illustrating the importance of probes, targets or surface interactions in biosensors. Interestingly, K_D^Surf values depend on the aptamer grafting density and linearly extrapolate towards K_D^Sol for highly diluted probes. This suggests a lesser impact of the surface compared to the probe or target cooperativity interactions since the latter decrease with a reduced grafting density.