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Surface chemistry is one of the most crucial aspects for microarray modality biosensor development. As a matter of fact, the immobilization capability of the functionalized surface is one of the limiting factors for the final yield of the binding reaction. In this work, we locally deposited many reactive polymers on a single solid support, allowing for a direct comparison of functionality of probes immobilized on different polymers and demonstrating a new way of multiplexing. Our goal was to investigate the immobilization efficiency of reactive polymers, as well as the resulting affinity of the molecular probes, in a single experiment. This idea was demonstrated by spotting a large number of different reactive polymers on an untreated Si/SiO2 chip, and depositing the same molecular probe on all the spots immediately after. This method proved to be efficient and could be used as an initial qualitative assay to decide which functionalization better suits a certain application. We also showed that the localized functionalization method is applicable to proteins as well as oligonucleotides. Moreover, by means of real-time binding measurements performed with the Interferometric Reflectance Imaging Sensor (IRIS), we demonstrated that this functionalization technique is comparable to the uniformity of classical flat-coating solution. The comparison between the binding curves that were obtained from different polymer spots with the same probe allowed us to decide which polymers would work better to immobilize a model protein, α-Lactalbumin, as well as a peptide extracted from the latter, namely LAC-1. The final outcome is promising, and it highlights the multiplexing power of this method: first, it allows to characterize dozens of polymers at once, within a single 60-minutes experiment. Secondly, it removes the limitation, related to coated surfaces, that only molecules with the same functional groups can be tethered to the same solid support. By applying this innovative protocol, there is no more restriction on the type of molecules that can be studied simultaneously and immobilization for each molecular probe can be individually optimized.

We use direct femtosecond laser writing to integrate optical waveguides into a commercial fused silica capillary electrophoresis chip. High-quality waveguides crossing the microfluidic channels are fabricated and used to optically address, with high spatial selectivity, their content. Fluorescence from the optically excited volume is efficiently collected at a 90 degree angle by a high numerical aperture fiber, resulting in a highly compact and portable device. To test the platform we performed electrophoresis and detection of a 23-mer oligonucleotide plug. Our approach is quite powerful because it allows the integration of photonic functionalities, by simple post-processing, into commercial LOCs fabricated with standard techniques.

We have recently introduced a silicon substrate for high-sensitivity microarrays, coated with a functional polymer named copoly(DMA-NAS-MAPS). The silicon dioxide thickness has been optimized to produce a fluorescence intensification due to the optical constructive interference between the incident and reflected lights of the fluorescent radiation. The polymeric coating efficiently suppresses aspecific interaction, making the low background a distinctive feature of these slides. Here, we used the new silicon microarray substrate for allergy diagnosis, in the detection of specific IgE in serum samples of subjects with sensitizations to inhalant allergens. We compared the performance of silicon versus glass substrates. Reproducibility data were measured. Moreover, receiver-operating characteristic (ROC) curves were plotted to discriminate between the allergy and no allergy status in 30 well-characterized serum samples. We found that reproducibility of the microarray on glass supports was not different from available data on allergen arrays, whereas the reproducibility on the silicon substrate was consistently better than on glass. Moreover, silicon significantly enhanced the performance of the allergen microarray as compared to glass in accurately identifying allergic patients spanning a wide range of specific IgE titers to the considered allergens.