Surface chemistry and morphology in single particle optical imaging

Abstract

Biological nanoparticles such as viruses and exosomes are important biomarkers for a range of medical conditions, from infectious diseases to cancer. Biological sensors that detect whole viruses and exosomes with high specificity, yet without additional labeling, are promising because they reduce the complexity of sample preparation and may improve measurement quality by retaining information about nanoscale physical structure of the bio-nanoparticle (BNP). Towards this end, a variety of BNP biosensor technologies have been developed, several of which are capable of enumerating the precise number of detected viruses or exosomes and analyzing physical properties of each individual particle. Optical imaging techniques are promising candidates among broad range of label-free nanoparticle detectors. These imaging BNP sensors detect the binding of single nanoparticles on a flat surface functionalized with a specific capture molecule or an array of multiplexed capture probes. The functionalization step confers all molecular specificity for the sensor's target but can introduce an unforeseen problem; a rough and inhomogeneous surface coating can be a source of noise, as these sensors detect small local changes in optical refractive index. In this paper, we review several optical technologies for label-free BNP detectors with a focus on imaging systems. We compare the surface-imaging methods including dark-field, surface plasmon resonance imaging and interference reflectance imaging. We discuss the importance of ensuring consistently uniform and smooth surface coatings of capture molecules for these types of biosensors and finally summarize several methods that have been developed towards addressing this challenge.

The Effects of Three-Dimensional Ligand Immobilization on Kinetic Measurements in Biosensors

“…One of the main limitations of label-free kinetics measurements is the requirement to immobilize one of the two interacting agents (the ligand) onto the sensor surface, in order to measure the amount of target analyte binding to the ligands. Consequently, the surface of the sensor needs to be chemically activated and functionalized by coating it with a specifically designed material containing reactive groups that can stably anchor molecules, without permanently denaturating their structure [10]. Moreover, such material needs to attach the probe molecules to form a high density layer while otherwise being repulsive to other non-specific interactions (anti-fouling).…”

“…With a huge dynamic range in analyte size ranging from small molecules [5] to extracellular vesicles [49], this technology has enabled kinetic characterization of hundreds of different molecules. The combination of the IRIS platform with the surface chemistry provided by the MCP polymers has produced significant results in molecular characterization and single particle detection [10,[50][51][52][53] with minimal instrumentation requirements [54].…”

The Role of Surface Chemistry in the Efficacy of Protein and DNA Microarrays for Label-Free Detection: An Overview

“…One of the main challenges when imaging single biological micro- and nano-particles is the capture efficiency of the active surface [ 85 ]. For the purpose of this discussion, we will focus on the capture and imaging of whole biological and synthetic particles onto multiplexed protein microarrays.…”

Configurable Digital Virus Counter on Robust Universal DNA Chips

“…A major challenge with antibody-based solid-phase biosensors is the immobilization of capture probes on the sensor surface. The surface attachment chemistry can affect the biological activity of the antibody, its affinity, and the background noise, ultimately affecting the sensitivity of the biosensor. − Moreover, printing of antibodies on the microarray surface can introduce issues such as nonuniform surface coverage and assay-to-assay variability, affecting the assay accuracy and reproducibility. − …”