Cell signaling activities play a critical role in physiological and disease processes. The analysis of the tumor microenvironment or the immune system activation is nowadays providing valuable insights towards disease understanding and novel therapies development. Due to the various dynamic profiles, it is essential to implement a continuous monitoring methodology for accurate analysis. The current fluorescent and colorimetric approaches hinder such applications due to their multiple time-consuming steps, molecular labeling, and the ‘snapshot’ endpoint readouts. Photonics technology, and especially nanoplasmonic biosensors offer a unique opportunity to implement lab-on-a-chip systems that provide highly sensitive and label-free analysis of cell signaling events in real time. Here, we will present a microfluidics-integrated nanoplasmonic biosensor for long-term and real-time monitoring of cell secretion activity. The biosensor consists of a gold nanohole array supporting extraordinary optical transmission (EOT), which has been optimized to enable ultra-sensitive and high-throughput biomolecular detection. The nanobiosensor is integrated with a specifically designed microfluidic system that provides well-controlled cell culture conditions for long-term monitoring. We achieved an outstanding sensitivity for the detection of vascular endothelial growth factor (VEGF) directly secreted from microfluidic-cultured cancer cells. We demonstrated real-time monitoring for over 10 hours, preserving good cell viability. The multiplexing capability of our nanobiosensor could enable simultaneous analysis of different cell types and molecules-of-interest. Thus, our innovative approach of probing live cells can be a powerful tool to evaluate cellular activities for diagnostics and novel therapy development.
The implementation of multiplexed point-of-care biosensors is a top priority to address the current epidemic problems originated by widespread pathogenic infections, like those caused by viruses or bacteria. A rapid and accurate detection, identification, and quantification of the infectious pathogens is essential not only to facilitate a prompt treatment but also to prevent onward transmission, reduce economic expenses, and significantly promote healthcare in resource-constrained environments. We have developed a nanoplasmonic biosensor based on nanohole arrays for fast and highly sensitive analysis in a simple and direct configuration. Our microarray is integrated into a microfluidic system to allow for highthroughput detection of multiple targets in a few minutes, without the need of sample pretreatment or amplification steps. Previously, we demonstrated the utility of the biosensor for the detection of hazardous live viruses, such as the Ebola or Vaccinia viruses, measured directly in biological media. Most recently we proved the truly multiplexing capability of our plasmonic microarray with the simultaneous identification and quantification of Chlamydia trachomatis and Neisseria gonorrhoeae in urine samples. We are able to detect and distinguish the two different bacteria with detection limits in the range of 102 -103 bacteria/mL. With recent advances in plasmonics, optimized surface chemistry, and microfluidics integration, our biosensors could provide a non-invasive and rapid diagnosis at the point of care, especially when we combine the detection on a compact and low-cost optical reader.
Nanohole array surface plasmon resonance (SPR) sensors offer a promising platform for high-throughput label-free biosensing. Integrating nanohole arrays with group-IV semiconductor photodetectors could enable low-cost and disposable biosensors compatible to Si-based complementary metal oxide semiconductor (CMOS) technology that can be combined with integrated circuitry for continuous monitoring of biosamples and fast sensor data processing. Such an integrated biosensor could be realized by structuring a nanohole array in the contact metal layer of a photodetector. We used Fouriertransform infrared spectroscopy to investigate nanohole arrays in a 100 nm Al film deposited on top of a vertical Si-Ge photodiode structure grown by molecular beam epitaxy (MBE). We find that the presence of a protein bilayer, constitute of protein AG and Immunoglobulin G (IgG), leads to a wavelength-dependent absorptance enhancement of ~ 8 %.
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