Microfluidics is revolutionizing the way research on cellular biology has been traditionally conducted. The ability to control the cell physicochemical environment by adjusting flow conditions, while performing cellular analysis at single-cell resolution and high-throughput, has made microfluidics the ideal choice to replace traditional in vitro models. However, such a revolution only truly started with the advent of polydimethylsiloxane (PDMS) as a microfluidic structural material and soft-lithography as a rapid manufacturing technology. Indeed, before the “PDMS age,” microfluidic technologies were: costly, time-consuming and, more importantly, accessible only to specialized laboratories and users. The simplicity of molding PDMS in various shapes along with its inherent properties (transparency, biocompatibility, and gas permeability) has spread the applications of innovative microfluidic devices to diverse and important biological fields and clinical studies. This review highlights how PDMS-based microfluidic systems are innovating pre-clinical biological research on cells and organs. These devices were able to cultivate different cell lines, enhance the sensitivity and diagnostic effectiveness of numerous cell-based assays by maintaining consistent chemical gradients, utilizing and detecting the smallest number of analytes while being high-throughput. This review will also assist in identifying the pitfalls in current PDMS-based microfluidic systems to facilitate breakthroughs and advancements in healthcare research.

In this work, we report all-silicon, integrated optofluidic microsystems (OFMs) fabricated by electrochemical micromachining (ECM) technology, in which high aspect-ratio (HAR) photonic crystal (PhC) devices (i.e. micromirrors, optical cavities) are integrated by one-etching-step, together with microfluidic reservoirs/channels, for the infiltration of liquids in the PhC air gaps, and with fiber grooves for alignment/positioning of readout optical fibers in front of the PhC, on the same silicon die. This has not previously been reported in the literature, and opens up new ground in, though not limited to, the optofluidics field, due to the low-cost and high-flexibility of the ECM technology that allows optofluidic microsystem fabrication to be performed in any lab. Optofluidic characterization of PhC-OFMs by both capillary-action and pressure-driven operations is carried out through the measurement of the reflectivity spectra of HAR-PhCs upon injection of liquids featuring different refractive index values in the HAR-PhC air gaps, by using readout optical fibers positioned in the on-chip fiber grooves. High sensitivity and good limit of detection of PhC-OFMs are obtained for both capillary-action and pressure-driven operations. A best sensitivity value of 670 nm/RIU and a worst-case limit of detection of the order of 10⁻³ RIU are measured, the former being comparable to state-of-the-art integrated refractive index sensors and the latter being limited by constraints of the experimental setup. The proof of concept about the biosensing potential of PhC-OFMs is given by successfully carrying out a sandwich assay based on antigen–antibody interactions for the detection of the C-reactive protein (CRP) at a concentration value of 10 mg L⁻¹, which represents the boundary level between physiological and pathological conditions.

Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use optical methods based on photonic nanojets, namely, needle-like beams featuring a nanometric width. In this review, we survey the physics, engineering strategies, and recent implementations of photonic nanojets for high-throughput generation of arbitrary nanopatterns, along with applications in optics, electronics, mechanics, and biosensing. An outlook of the potential impact of nanopatterning technologies based on photonic nanojets in several relevant biomedical areas is also provided.