Smart, Gravity-Driven, Dual-Mode, Disposable Evanescent Wave Fluorescent Optofluidic Bio-Nanochip for Rapid and Sensitive Point-of-Need Testing of Trace Pollutants.

Microfluidic–optical integrated portable platform with handheld pump for wash-free plasmonic detection of thrombin and SARS-CoV-2 spike protein

Point-of-care testing (POCT) requires rapid, quantitative results without the complexity of laboratory instrumentation. Conventional assays like ELISA and PCR are often limited by long processing times, multiple washing procedures, and a dependence on bulky, external power-consuming pumps. To address these challenges, we developed a fully integrated, palm-sized platform validated with two high-impact biomarkers: thrombin, a critical regulator of blood coagulation for cardiovascular and renal diagnostics, and the SARS-CoV-2 spike protein, a primary antigen for rapid viral screening. The platform’s innovation lies in its user-independent, electricity-free fluidic operation, featuring a manual suction pump with a compression spring that ensures high reproducibility (CV < 4.5%). Additionally, a serpentine microchannel design was incorporated to promote Dean flow-induced inertial mixing, accelerating aggregation kinetics for a true wash-free plasmonic assay. Our system provides real-time quantitative detection within 5 min, achieving sub-nanomolar limits of detection (LoD: 0.5 nM for thrombin and 0.4 nM for spike protein). Wireless connectivity allows for immediate data visualization on smartphones. By bridging the gap between sophisticated laboratory analysis and portable, manual operation, this platform offers a robust and scalable solution for decentralized clinical diagnostics.

Evanescent field techniques for nano-biosensing.

The relentless pursuit of rapid, ultrasensitive, and real-time analytical tools has positioned evanescent wave-based biosensors at the forefront of modern diagnostics. These platforms, which exploit the surface-confined electromagnetic field generated during total internal reflection, enable label-free, highly sensitive detection of biomolecular interactions. This review critically examines the recent advances in evanescent-wave-based analytical approaches for nanobiosensing, providing a comprehensive overview of the current research landscape and future perspectives. We delve into the predominant analytical platforms, including Surface Plasmon Resonance (SPR), Localized Surface Plasmon Resonance (LSPR), and various optical waveguide and fiber-optic configurations. A central focus is placed on the synergistic integration of nanomaterials, such as metallic nanoparticles, graphene and other 2D materials, and quantum dots, to enhance analytical performance through signal amplification and novel surface functionalities. Furthermore, we highlight current trends shaping the field's trajectory, including convergence with microfluidics to create Lab-on-a-Chip (LOC) systems for point-of-care (POC) applications, the deployment of machine learning for advanced data interpretation, and the development of portable, smartphone-integrated readers. Finally, the review addresses the persistent analytical challenges, including matrix effects, nonspecific binding, and manufacturing scalability, and provides a forward-looking perspective on the emerging materials and technologies poised to overcome these hurdles and redefine the future of bioanalytical science.

Free-Space–Coupled Frequency-Locked Microtoroid Sensors for Ultra-Sensitive Label-Free Chemical and Biological Detection

Whispering gallery mode (WGM) microresonators have emerged as powerful platforms for label-free chemical and biological sensing due to their ultra-high quality factors and strong evanescent field interactions. Frequency-locked optical whispering evanescent resonator (FLOWER) systems have demonstrated single-molecule sensitivity and zeptomolar detection limits in liquid environments. Conventional implementations, however, rely on tapered fiber coupling, which can limit robustness, scalability, and practical deployment. Here, we describe free-space–coupled frequency-locked microtoroid sensor architectures designed to eliminate fragile tapered fibers while maintaining high sensitivity. Free-space optical excitation of ultra-high-Q silica microtoroids provides a promising route toward compact and mechanically robust sensing platforms. We discuss the operating principles, system design considerations, and applications of these sensors for chemical and biological detection. These approaches may enable deployable WGM sensing systems for environmental monitoring, defense, and biomedical diagnostics.

Dual-Mode Microcantilever Sensor with Surface-Attached Nanofiber Membrane for Rapid and Highly Sensitive Detection of Ractopamine.

Scalable optical metasurfaces for ultrasensitive, label-free and real-time biosensing

Novel biosensors based on optical metasurfaces offer superior sensing performance in compact form factors, with transformative potential spanning biomedical research, clinical diagnostics and drug screening. However, their translation to real-world applications is hindered by a strong reliance on sophisticated and expensive top-down nanolithographic techniques with limited accessibility and low throughput. Here, we demonstrate scalable, high-throughput metasurfaces with optofluidic integration for label-free biosensing, exemplified by high-quality large-area gold nanohole arrays via nanosphere self-assembly lithography. Through comprehensive resonance analysis, we identified a surface plasmon polariton–Bloch wave mode that is both highly sensitive and experimentally accessible using cost-effective setups with incoherent visible light. Moreover, to improve the mass transport and analyte capture, we optimized the functionalization scheme, microfluidic design, and the metasurface placement within the microfluidic channel. The versatile meta-sensors were demonstrated with a broad range of targets, from biomolecules such as immunoglobulin G, streptavidin, to streptavidin-coated nanoparticles, which mimic virus particles and extracellular vesicles. By holistically improving the nanopatterning quality, functionalization efficiency and optofluidic integration, we achieved an experimental refractometric sensitivity of 498 nm/refractive index unit at 736 nm wavelength, a limit of detection of 0.17 ng/mL for biomolecules and ≲1 × 107 /mL for nanoparticles. These scalable, cost-effective meta-sensors deliver sensing performance, dynamic range, and stability comparable to, or even surpass, those of state-of-the-art devices fabricated using top-down lithography, thereby bridging the gap toward practical applications. Scalable, versatile optical sensors detect a broad range of biomolecules and particles without labels in real time. Integrated microfluidics boosts delivery and capture of rare targets on light-enhanced sensor surfaces. Sensors exceed leading devices while using low-cost, high-throughput manufacturing process and visible light setups. Cleanroom-free method makes advanced biosensing more accessible and affordable for real-world applications. Platform supports multiplexed, point-of-care, and potentially wearable or fiber-based clinical diagnostic tools. Scalable, versatile optical sensors detect a broad range of biomolecules and particles without labels in real time. Integrated microfluidics boosts delivery and capture of rare targets on light-enhanced sensor surfaces. Sensors exceed leading devices while using low-cost, high-throughput manufacturing process and visible light setups. Cleanroom-free method makes advanced biosensing more accessible and affordable for real-world applications. Platform supports multiplexed, point-of-care, and potentially wearable or fiber-based clinical diagnostic tools.

An Ultra-Sensitive QCM-Based Detecting Platform for On-Site and Rapid Quantification of Nanoplastics in Bottled Water.

The release of nanoplastics (NPs) from plastic bottled water containers has emerged as a concealed yet critical threat to water quality and consumer health. Yet, on-site and rapid quantification of NPs, particularly at environmentally relevant trace levels, remains a formidable analytical challenge. Here, we reported an ultrasensitive detection platform that integrates a quartz crystal microbalance (QCM) with a custom-engineered nanoporous sensing chip, enabling real-time, field-deployable quantification of NPs in bottled water with a detection limit of 0.39 μg·L-1. The platform achieves quantitative analysis of multiple NP types, including poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), poly(vinyl alcohol) (PVA), polyvinyl chloride (PVC), polystyrene (PS), and carboxylated PS (PS-COOH), with a surface mass sensitivity of 17.7 ng·cm-2·Hz-1. Comprehensive interfacial characterization, supported by molecular simulations, shows that electrostatic attraction facilitates initial NP capture, whereas van der Waals interactions stabilize the adsorbed state, with PET exhibiting particularly favorable adsorption energetics. Leveraging this mechanism, we then conceived a portable device and validated its performance across diverse real-world scenarios involving PET-contaminated bottled water. The system demonstrated robust reliability and analytical fidelity under field conditions. This work establishes a QCM-based analytical paradigm for NP quantification and delivers a deployable technological solution for on-site, rapid, and trustworthy monitoring of NPs in drinking water matrices.