Single-Particle Optical Imaging for Ultrasensitive Bioanalysis

Abstract

The quantitative detection of critical biomolecules and in particular low-abundance biomarkers in biofluids is crucial for early-stage diagnosis and management but remains a challenge largely owing to the insufficient sensitivity of existing ensemble-sensing methods. The single-particle imaging technique has emerged as an important tool to analyze ultralow-abundance biomolecules by engineering and exploiting the distinct physical and chemical property of individual luminescent particles. In this review, we focus and survey the latest advances in single-particle optical imaging (OSPI) for ultrasensitive bioanalysis pertaining to basic biological studies and clinical applications. We first introduce state-of-the-art OSPI techniques, including fluorescence, surface-enhanced Raman scattering, electrochemiluminescence, and dark-field scattering, with emphasis on the contributions of various metal and nonmetal nano-labels to the improvement of the signal-to-noise ratio. During the discussion of individual techniques, we also highlight their applications in spatial–temporal measurement of key biomarkers such as proteins, nucleic acids and extracellular vesicles with single-entity sensitivity. To that end, we discuss the current challenges and prospective trends of single-particle optical-imaging-based bioanalysis.

Recent Developments in Single-Entity Electrochemistry

“…Optical microscopy has proven an ideal tool for nondestructively and nonintrusively studying SEs in biological and material applications. − The diversity of optical techniques, each with strengths and limitations, allows for flexibility in experimental design, making optical approaches to study SEs highly versatile . Further, the wide-field nature and high spatiotemporal resolution of optical microscopy allows for multiple SE processes to be monitored simultaneously, allowing for statistical analysis that reveals heterogeneous distributions and behaviors not captured in ensemble studies. − In tandem with SE electrochemistry methods, optical microscopy can be used to provide new, complementary information that can be hidden in electrochemical measurements alone, providing greater insight. − In the simplest form of SE opto-electrochemistry, optical microscopy is used to monitor and/or provide real-time time feedback about electrochemical-driven reactions and processes .…”

An extracellular vesicle microRNA-initiated 3D DNAzyme motor for colorectal cancer diagnosis

“…[25][26][27][28] Single molecule imaging is a promising technique for the ultrasensitive quantitative analysis of trace molecules in complex environments, which has the advantages of high precision, high signal-to-noise ratio, strong robustness against background fluctuations, multiplexing capability based on multiple fluorescent channels and the intuitiveness of visualization. 29,30 Based on the features above, it is convincing that the integration of DNAzyme motors and a single molecule imaging technique has great potential to enable the highly sensitive analysis of multiple miRNAs in a more intuitive and concise way.…”