Microrings for microRNAs! A label‐free method has been developed for the sensitive detection of microRNAs utilizing arrays of silicon photonic microring resonators. This simple and modularly multiplexable method for the direct profiling of microRNA within 10 minutes meets a number of challenges faced by current methodologies in this area.

In this paper, we present a method for the ultrasensitive detection of microRNAs (miRNAs) utilizing an antibody that specifically recognizes DNA:RNA heteroduplexes, using a silicon photonic microring resonator array transduction platform. Microring resonator arrays are covalently functionalized with DNA capture probes that are complementary to solution phase miRNA targets. Following hybridization on the sensor, the anti-DNA:RNA antibody is introduced and binds selectively to the heteroduplexes, giving a larger signal than the original miRNA hybridization due to the increased mass of the antibody, as compared to the 22 oligoribonucleotide. Furthermore, the secondary recognition step is performed in neat buffer solution and at relatively higher antibody concentrations, facilitating the detection of miRNAs of interest. The intrinsic sensitivity of the microring resonator platform coupled with the amplification provided by the anti-DNA:RNA antibodies allows for the detection of microRNAs at concentrations as low as 10 pM (350 attomoles). The simplicity and sequence generality of this amplification method position it as a promising tool for high-throughput, multiplexed miRNA analysis, as well as a range of other RNA based detection applications.

Summary Optical whispering-gallery mode (WGM) microresonators, confining resonant photons in a microscale volume for long periods of time, strongly enhance light-matter interactions, making them an ideal platform for photonic sensors. One of the features of WGM sensors is their capability to respond to environmental perturbations that influence the optical mode distribution. The exceptional sensitivity of WGM devices, coupled with the diversity in their structures and the ease of integration with existing infrastructures, such as conventional chip-based technologies, has catalyzed the development of WGM sensors for a broad range of analytes. WGM sensors have been developed for multiplexed detection of clinically relevant biomolecules while also being adapted for the analysis of single-protein interactions. They have been used for the detection of materials in different phases and forms, including gases, liquids, and chemicals. Furthermore, WGM sensors have been used for a wide variety of field-based sensing applications, including electric field, magnetic field, force, pressure, and temperature. WGM sensors hold great potential for applications in life and environmental sciences. They are expected to meet the ever-increasing demand in sensor networks, the Internet of Things, and real-time health monitoring. Here we review the mechanisms, structures, parameters, and recent advances of WGM microsensors and discuss the future of this exciting research field.

In the post-genomic era, information is king and information-rich technologies are critically important drivers in both fundamental biology and medicine. It is now known that single-parameter measurements provide only limited detail and that quantitation of multiple biomolecular signatures can more fully illuminate complex biological function. Label-free technologies have recently attracted significant interest for sensitive and quantitative multiparameter analysis of biological systems. There are several different classes of label-free sensors that are currently being developed both in academia and in industry. In this critical review, we highlight, compare, and contrast some of the more promising approaches. We will describe the fundamental principles of these different methodologies and discuss advantages and disadvantages that might potentially help one in selecting the appropriate technology for a given bioanalytical application.

Nucleocapsid (N) encoded by SARS-CoV-2 plays key roles in the replication cycle and is a critical serological marker. Here we characterize essential biochemical properties of N and describe the utility of these insights in serological studies. We define N domains important for oligomerization and RNA binding and show that N oligomerization provides a high affinity RNA binding platform. We also map the RNA binding interface, showing protection in the N-terminal domain and linker region. In addition, phosphorylation causes reduction of RNA binding and redistribution of N from liquid droplets to loose-coils, showing how N/RNA accessibility and assembly may be regulated by phosphorylation. Finally, we find that the C-terminal domain of N is the most immunogenic, based upon antibody binding to patient samples. Together, we provide a biochemical description of SARS-CoV-2 N and highlight the value of using N domains as highly specific and sensitive diagnostic markers.

We report a sensitive, label-free method for detecting single-stranded DNA and discriminating between single nucleotide polymorphisms (SNPs) using arrays of silicon photonic microring resonators. In only a 10 minute assay, DNA is detected at sub-picomole levels with a dynamic range of three orders of magnitude. Following quantitation, sequence discrimination with single nucleotide resolution is achieved isothermally by monitoring the dissociation kinetics of the duplex in real-time using an array of SNP-specific capture probes. By leveraging the multiplexed capabilities of the microring resonator platform, we successfully generate multiplexed arrays to quickly screen for the presence and identity of SNPs and show the robustness of this methodology by analyzing multiple target sequences of varying GC content. Furthermore, we show that this technique can be used to distinguish both homozygote and heterozygote alleles.

In less than 20 years, our appreciation for micro-RNA molecules (miRNAs) has grown from an original, curious observation in worms to their current status as incredibly important global regulators of gene expression that play key roles in many transformative biological processes. As our understanding of these small, non-coding transcripts continues to evolve, new approaches for their analysis are emerging. In this critical review we describe recent improvements to classical methods of detection as well as innovative new technologies that are poised to help shape the future landscape of miRNA analysis.

The detection of biomolecules at ultralow (low to subpicogram per milliliter) concentrations and within complex, clinically relevant matrices is a formidable challenge that is complicated by limitations imposed by the Langmuir binding isotherm and mass transport, for surface-based affinity biosensors. Here we report the integration of an enzymatic signal enhancement scheme onto a multiplexable silicon photonic microring resonator detection platform. To demonstrate the analytical value of this combination, we simultaneously quantitated levels of the interleukins IL-2, IL-6, and IL-8 in undiluted cerebrospinal fluid in an assay format that is multiplexable, relatively rapid (90 min), and features a 3 order of magnitude dynamic range and a limit of detection ≤1 pg/mL. The modular nature of this assay and technology should lend itself broadly amenable to different analyte classes, making it a versatile tool for biomarker analysis in clinically relevant settings.