Optical Sensing Strategies for Probing Single-Cell Secretion

Machine Learning-Driven SERS Nanoendoscopy and Optophysiology

A frontier of analytical sciences is centered on the continuous measurement of molecules in or near cells, tissues, or organs, within the biological context in situ, where the molecular-level information is indicative of health status, therapeutic efficacy, and fundamental biochemical function of the host. Following the completion of the Human Genome Project, current research aims to link genes to functions of an organism and investigate how the environment modulates functional properties of organisms. New analytical methods have been developed to detect chemical changes with high spatial and temporal resolution, including minimally invasive surface-enhanced Raman scattering (SERS) nanofibers using the principles of endoscopy (SERS nanoendoscopy) or optical physiology (SERS optophysiology). Given the large spectral data sets generated from these experiments, SERS nanoendoscopy and optophysiology benefit from advances in data science and machine learning to extract chemical information from complex vibrational spectra measured by SERS. This review highlights new opportunities for intracellular, extracellular, and in vivo chemical measurements arising from the combination of SERS nanosensing and machine learning.

Integration of 2D Nanoporous Membranes in Microfluidic Devices

2D material-based membranes have emerged as promising candidates for next-generation separation technology due to their exceptional permeability and selectivity. Integration of these membranes into microfluidic devices has offered significant potential for improving the efficiency, throughput, and precision. However, designing compact and reliable microfluidic devices with membranes has many challenges, including complexities in membrane integration, analyte measurement, and contamination issues. Addressing these challenges is critical for unlocking the full potential of membrane-integrated devices. This paper proposes a systematic procedure for integrating membranes into a microfluidic device by creating a pore in the middle layer. Furthermore, an ion transport experiment is carried out across various stacked graphene and poly carbonate track etch membranes in an Ostemer-based device. The resulting device is capable of facilitating the concurrent measurement, a task that is cumbersome in standard macroscopic diffusion cells. The transparency and compactness of the microfluidic device allowed for the in situ and real-time optical characterization of analytes. The integration of microfluidic devices with 2D nanoporous membranes has enabled the incorporation of several analytical modalities, resulting in a highly versatile platform with numerous applications.

Single-Cell Caspase-3 Measurement Using a Biomimetic Nanochannel

Direct single-cell caspase-3 (Casp-3) analysis has remained challenging. A study of single-cell Casp-3 could contribute to revealing the fundamental pathogenic mechanisms in Casp-3-associated diseases. Here, a biomimetic nanochannel capable of single-cell sampling and ionic detection of intracellular Casp-3 is devised, which is established upon the installment of target-specific organic molecules (luc-DEVD) within the orifice of a glass nanopipette. The specific cleavage of luc-DEVD by Casp-3 could induce changes of inner-surface chemical groups and charge properties, thus altering the ionic response of the biomimetic nanochannel for direct Casp-3 detection. The practical applicability of this biomimetic nanochannel is confirmed by probing intracellular Casp-3 fluctuation upon drug stimulation and quantifying the Casp-3 evolution during induced apoptosis. This work realizes ionic single-cell Casp-3 analysis and provides a different perspective for single-cell protein analysis.

Recent advancements in single-cell metabolic analysis for pharmacological research

Cellular heterogeneity is crucial for understanding tissue biology and disease pathophysiology. Pharmacological research is being advanced by single-cell metabolic analysis, which offers a technique to identify variations in RNA, proteins, metabolites, and drug molecules in cells. In this review, the recent advancement of single-cell metabolic analysis techniques and their applications in drug metabolism and drug response are summarized. High-precision and controlled single-cell isolation and manipulation are provided by microfluidics-based methods, such as droplet microfluidics, microchamber, open microfluidic probe, and digital microfluidics. They are used in tandem with variety of detection techniques, including optical imaging, Raman spectroscopy, electrochemical detection, RNA sequencing, and mass spectrometry, to evaluate single-cell metabolic changes in response to drug administration. The advantages and disadvantages of different techniques are discussed along with the challenges and future directions for single-cell analysis. These techniques are employed in pharmaceutical analysis for studying drug response and resistance pathway, therapeutic targets discovery, and in vitro disease model evaluation.