Coherent silicon photonic interferometric biosensor with an inexpensive laser source for sensitive label-free immunoassays.

Over the past two decades, integrated photonic sensors have been of major interest to the optical biosensor community due to their capability to detect low concentrations of molecules with label-free operation. Among these, interferometric sensors can be read-out with simple, fixed-wavelength laser sources and offer excellent detection limits but can suffer from sensitivity fading when not tuned to their quadrature point. Recently, coherently detected sensors were demonstrated as an attractive alternative to overcome this limitation. Here we show, for the first time, to the best of our knowledge, that this coherent scheme provides sub-nanogram per milliliter limits of detection in C-reactive protein immunoassays and that quasi-balanced optical arm lengths enable operation with inexpensive Fabry-Perot-type lasers sources at telecom wavelengths.

Real-time monitoring of fenitrothion in water samples using a silicon nanophotonic biosensor.

Due to the large quantities of pesticides extensively used and their impact on the environment and human health, a prompt and reliable sensing technique could constitute an excellent tool for in-situ monitoring. With this aim, we have applied a highly sensitive photonic biosensor based on a bimodal waveguide interferometer (BiMW) for the rapid, label-free, and specific quantification of fenitrothion (FN) directly in tap water samples. After an optimization protocol, the biosensor achieved a limit of detection (LOD) of 0.29 ng mL-1 (1.05 nM) and a half-maximal inhibitory concentration (IC50) of 1.71 ng mL-1 (6.09 nM) using a competitive immunoassay and employing diluted tap water. Moreover, the biosensor was successfully employed to determine FN concentration in blind tap water samples obtaining excellent recovery percentages with a time-to-result of only 20 min without any sample pre-treatment. The features of the biosensor suggest its potential application for real time, fast and sensitive screening of FN in water samples as an analytical tool for the monitoring of the water quality.

Label-Free and Real-Time Detection of Tuberculosis in Human Urine Samples Using a Nanophotonic Point-of-Care Platform.

Tuberculosis (TB) is the leading global cause of death from a single infectious agent. Registered incidence rates are low, especially in low-resource countries with weak health systems, due to the disadvantages of current diagnostic techniques. A major effort is directed to develop a point-of-care (POC) platform to reduce TB deaths with a prompt and reliable low-cost technique. In the frame of the European POCKET Project, a novel POC platform for the direct and noninvasive detection of TB in human urine was developed. The photonic sensor chip is integrated in a disposable cartridge and is based on a highly sensitive Mach-Zehnder Interferometer (MZI) transducer combined with an on-chip spectral filter. The required elements for the readout are integrated in an instrument prototype, which allows real-time monitoring and data processing. In this work, the novel POC platform has been employed for the direct detection of lipoarabinomannan (LAM), a lipopolysaccharide found in the mycobacterium cell wall. After the optimization of several parameters, a limit of detection of 475 pg/mL (27.14 pM) was achieved using a direct immunoassay in undiluted human urine in less than 15 min. A final validation of the technique was performed using 20 clinical samples from TB patients and healthy donors, allowing the detection of TB in people regardless of HIV coinfection. The results show excellent correlation to those obtained with standard techniques. These promising results demonstrate the high sensitivity, specificity and applicability of our novel POC platform, which could be used during routine check-ups in developing countries.