One-Shot Dual-Code Immunotargeting for Ultra-Sensitive Tumor Necrosis Factor-α Nanosensors by 3D Enhanced Dark-Field Super-Resolution Microscopy

Individual Plasmonic Nanoprobes for Biosensing and Bioimaging: Recent Advances and Perspectives

With the advent of nanofabrication techniques, plasmonic nanoparticles (PNPs) have been widely applied in various research fields ranging from photocatalysis to chemical and bio-sensing. PNPs efficiently convert chemical or physical stimuli in their local environment into optical signals. PNPs also have excellent properties, including good biocompatibility, large surfaces for the attachment of biomolecules, tunable optical properties, strong and stable scattering light, and good conductivity. Thus, single optical biosensors with plasmonic properties enable a broad range of uses of optical imaging techniques in biological sensing and imaging with high spatial and temporal resolution. This work provides a comprehensive overview on the optical properties of single PNPs, the description of five types of commonly used optical imaging techniques, including surface plasmon resonance (SPR) microscopy, surface-enhanced Raman scattering (SERS) technique, differential interference contrast (DIC) microscopy, total internal reflection scattering (TIRS) microscopy, and dark-field microscopy (DFM) technique, with an emphasis on their single plasmonic nanoprobes and mechanisms for applications in biological imaging and sensing, as well as the challenges and future trends of these fields.

Supersensitive Detection of the Norovirus Immunoplasmon by 3D Total Internal Reflection Scattering Defocus Microscopy with Wavelength-Dependent Transmission Grating

Norovirus (NoV) is a major foodborne pathogen, and even low levels of virus can cause infection and gastroenteritis. We developed a supersensitive NoV sensor that detects NoV group-I capsid protein (NoVP) via three-dimensional (3D) total internal reflection scattering defocus microscopy (TIRSDM) with wavelength-dependent transmission grating (TG). The combination of evanescent wave scattering and TG significantly enhanced the detection sensitivity and selectivity of NoVP in first-order spectral images (n = +1) by minimizing spectroscopic interference and background noise. In particular, wavelength-dependent 3D defocused TG imaging (3D TG-TIRSDM) separated silver nanotag and gold nanoplate signals on a NoVP immunoplasmon chip along the x, y, and z coordinates simultaneously. Additionally, the use of wavelength-dependent TG increased the spectral resolution by 5-fold along the xy-axis and 1.4-fold along the z-axis compared to conventional 3D TIRSDM at the subdiffraction limit. The NoVP sensor exhibited a lower limit of detection of 820 yM, which is 29 000 times better than the previous potentiometer method, and a wide dynamic detection range of 820 yM to 92.45 pM (R = 0.9801). This new method could be applied to detect various pathogenic viruses during the initial stage of infection.

Plasmon-Amplified Endogenous Fluorescence Nanospectroscopic Sensor Based on Inherent Elastic Scattering for Ultratrace Ratiometric Detection of Capsaicinoids

Endogenous fluorescence imaging techniques are key for modern single-molecule quantification without the use of additional labeling probes. However, the drawback of weak fluorescence signal is the primary challenge in meeting the ever-increasing demands of single-molecule detection. Here, we report a simple and reliable method that provides up to ∼100-fold uniform fluorescence enhancement of endogenous fluorescence of the capsaicinoid molecule. The method is based on a single nanoparticle plasmon-amplified endogenous fluorescence nanospectroscopic sensor (PAEFS). This work demonstrated the applicability of PAEFS in refining sensitivity at the single-molecule level by showing ultralow limits of detection (10⁶ times lower than previous reports) of fluorescence-based capsaicinoids with a wide range of linear response (18 zM to 85 pM). Spectrally overlapped capsaicinoid analogues were quantified ratiometrically to detect the analogue percentages in real samples. The novel endogenous fluorescence enhancement approach presented here represents a universal sensor for enhanced detection of single molecules using existing techniques without altering the original molecular features or using add-on labeling probes.

A single gold nanoprobe for colorimetric detection of silver(i) ions with dark-field microscopy

In this work, the formation of C–Ag⁺–C bonding between cytosines was utilized to induce interparticle coupling of gold nanoparticles modified with single-strand DNA, resulting in a color change as the signal transduction to quantify Ag⁺ sensitively under dark-field microscopy imaging, while we achieved the quantification of Ag⁺ could be directly realized in lake water samples and drug samples.