Sensitivity-enhanced localized surface plasmon resonance biosensing format dedicated for point-of-care testing tools

The main requirement for a point-of-care health monitoring tools is that it should involve relatively simple and inexpensive equipment ensuring acceptable accuracy of diseases early diagnostic. Quite commonly in practice, their main function is only to trigger an ‘alarm’ signal, when a specific biomarker of disease is detected in the sample. The affinity label-free biosensing involving surface plasmonic resonance (SPR) phenomena appears to be one of the most appropriate approaches for the above requirements. In our research, we focus on theoretical and experimental investigations of optional plasmonic-related biosensing formats easy to be integrated in lab-on-chip devices involving conventional planar SPR biosensing. One of such detection formats, mentioned in our earliest publications, involves localized surface plasmon resonance (LSPR) spectroscopy at the frustrated total internal reflection conditions (LSPR_TIR). In this paper, we report on the numerical and experimental study of LSPR_TIR spectroscopy of gold nanoparticles (NPs) structures with a relatively high density of NPs, manufactured using two different microfabrication methods: the conventional nano-sphere lithography, and the original one, involving the direct pulse laser writing. The last technology, developed by our research team, provides powerful and cost effective tools for flexible patterning of the disposable multichannel biochip with array of SPR and LSPR probes. The obtained results demonstrate a significant improvement in the LSPR wavelength sensitivity to sample refractive index. In addition, experimental investigations reveal a relatively efficient conversion of the incident light wave polarization that can be attributed to a relatively high efficiency of electromagnetic coupling between closely spaced NPs.