Nanoscale fluorescence emitters are efficient for measuring biomolecular interactions, but their utility for applications requiring single-unit observations is constrained by the need for large numerical aperture objectives, fluorescence intermittency, and poor photon collection efficiency resulting from omnidirectional emission. Photonic crystal (PC) structures hold promise to address the aforementioned challenges in fluorescence enhancement. In this review, we provide a broad overview of PCs by explaining their structures, design strategies, fabrication techniques, and sensing principles. Furthermore, we discuss recent applications of PC-enhanced fluorescence-based biosensors incorporated with emerging technologies, including nucleic acids sensing, protein detection, and steroid monitoring. Finally, we discuss current challenges associated with PC-enhanced fluorescence and provide an outlook for fluorescence enhancement with photonic-plasmonics coupling and their promise for point-of-care biosensing as well monitoring analytes of biological and environmental relevance. The review presents the transdisciplinary applications of PCs in the broad arena of fluorescence spectroscopy with broad applications in photo-plasmonics, life science research, materials chemistry, cancer diagnostics, and internet of things.

DNA has shown great biocompatibility, programmable mechanical properties, and precise structural addressability at the nanometer scale, rendering it a material for constructing versatile nanorobots for biomedical applications. Here, we present the design principle, synthesis, and characterization of a DNA nanorobotic hand, called DNA NanoGripper, that contains a palm and four bendable fingers as inspired by naturally evolved human hands, bird claws, and bacteriophages. Each NanoGripper finger consists of three phalanges connected by three rotatable joints that are bendable in response to the binding of other entities. NanoGripper functions are enabled and driven by the interactions between moieties attached to the fingers and their binding partners. We demonstrate that the NanoGripper can be engineered to effectively interact with and capture nanometer-scale objects, including gold nanoparticles, gold NanoUrchins, and SARS-CoV-2 virions. With multiple DNA aptamer nanoswitches programmed to generate a fluorescent signal that is enhanced on a photonic crystal platform, the NanoGripper functions as a highly sensitive biosensor that selectively detects intact SARS-CoV-2 virions in human saliva with a limit of detection of ~100 copies per milliliter, providing a sensitivity equal to that of reverse transcription quantitative polymerase chain reaction (RT-qPCR). Quantified by flow cytometry assays, we demonstrated that the NanoGripper-aptamer complex can effectively block viral entry into the host cells, suggesting its potential for inhibiting virus infections. The design, synthesis, and characterization of a sophisticated nanomachine that can be tailored for specific applications highlight a promising pathway toward feasible and efficient solutions to the detection and potential inhibition of virus infections.

Convergent framework for future POC cancer diagnostics aligning clinical needs (why), enabling technologies (how), and translational bridges. It integrates lab-on-chip biosensing and analytics for decentralized, early, longitudinal care.

Hybridizing fluorescent reporters with gold nanoparticles (AuNPs) presents challenges associated with surface‐induced quenching in the “zone of inactivity,” compromising the functionality of related point‐of‐care diagnostic tools. Nano‐assembly of high refractive index (HRI) dielectric and plasmonic NPs yields augmented electric and magnetic resonances that are not achievable with the individual counterparts. Here, several long‐standing challenges associated with conventional photon‐emitting reporters are addressed by integrating HRI dielectric fluorescent nanodiamonds (NDs) with metallo‐dielectric nano‐assemblies. An adiabatic cooling (−196 °C) driven nano‐assembly method is used to synthesize AuND cryosoret (AuNDCS) nano‐assemblies. More than 600‐fold enhancement of the emission from the nitrogen vacancy of AuNDCS is demonstrated when interfaced with a photonic crystal through interaction with the radiating guided mode resonance. Experimental results are corroborated with extensive simulations of a variety of nano‐constructs, including monomers (0D), dimers (1D), trimers (2D), and tetramers (3D) to visualize the electric and magnetic field hotspots. The fluorescence enhancement is utilized to detect a cancer‐specific target biomarker, micro‐RNA 375, with femtomolar‐level detection limits, using the AuNDCS as a molecular tag. The PC‐enhanced fluorescence detection instrument does not require prisms, objectives, or cooled photodetectors, resulting in a compact and inexpensive system that would be suitable for environments outside of conventional diagnostic laboratories.