A critical review of advances in surface plasmon resonance imaging sensitivity

Recent advancements of smartphone-based sensing technology for diagnosis, food safety analysis, and environmental monitoring

The emergence of computationally powerful smartphones, relatively affordable high-resolution camera, drones, and robotic sensors have ushered in a new age of advanced sensible monitoring tools. The present review article investigates the burgeoning smartphone-based sensing paradigms, including surface plasmon resonance (SPR) biosensors, electrochemical biosensors, colorimetric biosensors, and other innovations for modern healthcare. Despite the significant advancements, there are still scarcity of commercially available smart biosensors and hence need to accelerate the rates of technology transfer, application, and user acceptability. The application/necessity of smartphone-based biosensors for Point of Care (POC) testing, such as prognosis, self-diagnosis, monitoring, and treatment selection, have brought remarkable innovations which eventually eliminate sample transportation, sample processing time, and result in rapid findings. Additionally, it articulates recent advances in various smartphone-based multiplexed bio sensors as affordable and portable sensing platforms for point-of-care devices, together with statistics for point-of-care health monitoring and their prospective commercial viability.

Surface Plasmon Resonance Biosensors: A Review of Molecular Imaging with High Spatial Resolution

Surface plasmon resonance (SPR) is a powerful tool for determining molecular interactions quantitatively. SPR imaging (SPRi) further improves the throughput of SPR technology and provides the spatially resolved capability for observing the molecular interaction dynamics in detail. SPRi is becoming more and more popular in biological and chemical sensing and imaging. However, SPRi suffers from low spatial resolution due to the imperfect optical components and delocalized features of propagating surface plasmonic waves along the surface. Diverse kinds of approaches have been developed to improve the spatial resolution of SPRi, which have enormously impelled the development of the methodology and further extended its possible applications. In this minireview, we introduce the mechanisms for building a high-spatial-resolution SPRi system and present its experimental schemes from prism-coupled SPRi and SPR microscopy (SPRM) to surface plasmonic scattering microscopy (SPSM); summarize its exciting applications, including molecular interaction analysis, molecular imaging and profiling, tracking of single entities, and analysis of single cells; and discuss its challenges in recent decade as well as the promising future.

Recent advances in surface plasmon resonance imaging and biological applications

Surface Plasmon Resonance Imaging (SPRI) is a robust technique for visualizing refractive index changes, which enables researchers to observe interactions between nanoscale objects in an imaging manner. In the past period, scholars have been attracted by the Prism-Coupled and Non-prism Coupled configurations of SPRI and have published numerous experimental results. This review describes the principle of SPRI and discusses recent developments in Prism-Coupled and Non-prism Coupled SPRI techniques in detail, respectively. And then, major advances in biological applications of SPRI are reviewed, including four sub-fields (cells, viruses, bacteria, exosomes, and biomolecules). The purpose is to briefly summarize the recent advances of SPRI and provide an outlook on the development of SPRI in various fields.

Label-free OIRD microarray chips with a nanostructured sensing interface: enhanced sensitivity and mechanism

Oblique-incidence reflectivity difference (OIRD) is a novel optical technique for protein microarray detection with the characteristics of being real-time, label-free, high-throughput and compatible with arbitrary chip substrates. It is necessary yet challenging to improve the sensitivity of the OIRD microarray and gain a clear understanding of the enhancement mechanism for practical applications. In this study, we report a microarray chip specifically designed for OIRD to improve its sensitivity by using an electrochemically etched nanostructured fluorine-doped tin oxide (FTO) slide as the substrate. Compared with chips printed on a conventional glass slide and pristine FTO, the OIRD sensitivity and signal-to-noise ratio of this microarray are significantly improved, reaching a limit of detection (LOD) as low as 50 ng mL^-1 for the streptavidin target in 10% human serum, which is one order of magnitude lower than that of the glass-based chip. On-chip ELISA and theoretical calculation reveal that the enhanced sensitivity is not only because of its higher capture efficiency towards the target, but also benefits from the optical enhancement enabled by its unique nanostructured sensing interface. This work provides a new universal strategy for designing high performance OIRD-based chips via rational interfacial engineering, thus paving the way to a label-free OIRD immunoassay and real-time analysis of biomolecular interactions.

Carbohydrate microarrays fabricated on poly(2-methylacrylic acid)-based substrates for analysis of carbohydrate–protein interactions

Carbohydrate microarrays were fabricated on poly(2-methylacrylic acid) (pMAA)-based substrates. They were used for investigating the specific interactions of polysaccharides and SARS-CoV-2 spike protein.

Multiplexed, High-Sensitivity Measurements of Antibody Affinity Using Interferometric Reflectance Imaging Sensor

Anthrax lethal factor (LF) is one of the enzymatic components of the anthrax toxin responsible for the pathogenic responses of the anthrax disease. The ability to screen multiplexed ligands against LF and subsequently estimate the effective kinetic rates (kon and koff) and complementary binding behavior provides critical information useful in diagnostic and therapeutic development for anthrax. Tools such as biolayer interferometry (BLI) and surface plasmon resonance imaging (SPRi) have been developed for this purpose; however, these tools suffer from limitations such as signal jumps when the solution in the chamber is switched or low sensitivity. Here, we present multiplexed antibody affinity measurements obtained by the interferometric reflectance imaging sensor (IRIS), a highly sensitive, label-free optical biosensor, whose stability, simplicity, and imaging modality overcomes many of the limitations of other multiplexed methods. We compare the multiplexed binding results obtained with the IRIS system using two ligands targeting the anthrax lethal factor (LF) against previously published results obtained with more traditional surface plasmon resonance (SPR), which showed consistent results, as well as kinetic information previously unattainable with SPR. Additional exemplary data demonstrating multiplexed binding and the corresponding complementary binding to sequentially injected ligands provides an additional layer of information immediately useful to the researcher.

Bioinspired Virus-like Fe3O4/Au@C Nanovector for Programmable Drug Delivery via Hierarchical Targeting

Bioinspired strategies have recently emerged as novel approaches for designing a functionalized nanovector with enhanced tumor targeting and therapeutic efficacy. Herein, a virus-like Fe₃O₄/Au@C nanovector is described for programmable drug delivery via hierarchical targeting. Specifically, the virus-like Fe₃O₄/Au@C nanovector is synthesized via a simple hydrothermal process, and then the spiky surface of which is camouflaged via doxorubicin (DOX)-conjugated polyethylene glycol (PEG), constructing an innovative virus-like core/spherical shell biomimetic nanomedicine (Fe₃O₄/Au@C-DOX-PEG), which is conducive to improve bioavailability and reduce adverse effects. After systemic administration, the as-prepared nanomedicine is capable of facilitating effective tumor accumulation and deep tumor penetration with the assistance of an external magnetic field and endogenous pH stimuli. Simultaneously, in response to the acidic tumor microenvironment, Fe₃O₄/Au@C-DOX nanocomposites are released and exhibit excellent performance in cellular internalization through a virus-mimetic rough surface. Furthermore, the in vivo experiments identify that the unique nanomedicine is bestowed with an effective targeting tumor, prominent antitumor efficacy, and reduced systemic toxicity. Such a bioinspired hierarchical targeting nanoplatform holds promising potential for enhanced chemotherapeutic intracellular delivery and tumor theranostics.

Label-free methods for optical in vitro characterization of protein-protein interactions

Protein-protein interactions are involved in the regulation and function of the majority of cellular processes. As a result, much effort has been aimed at the development of methodologies capable of quantifying protein-protein interactions, with label-free methods being of particular interest due to the associated simplified workflows and minimisation of label-induced perturbations. Here, we review recent advances in optical technologies providing label-free in vitro measurements of affinities and kinetics. We provide an overview and comparison of existing techniques and their principles, discussing advantages, limitations, and recent applications.

UiO-66 metal-organic frameworks/gold nanoparticles based substrates for SERS analysis of food samples

Recently, metal-organic frameworks (MOFs) based substrates have shown great potential for the quantitative analysis of food samples by surface-enhanced Raman scattering (SERS) due to their unique properties. Herein, we developed two UiO-66 MOFs/gold nanoparticles (AuNPs) based substrates by self-assembly, including UiO-66/AuNPs suspension substrate and UiO-66(NH₂)/AuNPs/Nylon-66 flexible membrane substrate, for quantitative analysis of complex food samples by SERS. UiO-66/AuNPs suspension substrate was prepared for SERS-based determination of a carcinogenic heterocyclic amine in barbecue meat. UiO-66(NH₂)/AuNPs/Nylon-66 membrane substrate was fabricated for the simultaneous separation, enrichment, and in situ analysis of Sudan Red 7B in chilli products. The heterocyclic amine and Sudan dye in real samples could be detected and quantified with the recoveries of 82.3-110% and 84.5-114% and relative standard deviations (RSDs) of 3.1-11.0% and 1.9-5.6% (n = 3) by use of these two substrates, respectively. These two UiO-66/AuNPs based substrates combined molecular enrichment and SERS activity, achieving excellent analytical accuracy and widening SERS application in practical food safety analysis.

Multi-channel surface plasmon resonance biosensor using prism-based wavelength interrogation

A portable multi-channel surface plasmon resonance (SPR) biosensor device using prism-based wavelength interrogation is presented. LEDs were adopted as a simple and inexpensive light source, providing a stable spectrum bandwidth for the SPR system. The parallel light was obtained by a collimated unit and illuminated on the sensing chip at a specific angle. A simple, compact and cost-effective spectrometer part constituted of a series of lenses and a prism was designed for the collection of reflected light. Using the multi-channel microfluidic chip as the sensing component, spectral images of multiple tests could be acquired simultaneously, improving the signal processing and detection throughput. Different concentrations of sodium chloride aqueous solution were used to calibrate the device. The linear detection range was 4.32 × 10^-2 refractive index units (RIU) and the limit of detection was 6.38 × 10^-5 RIU. Finally, the performance of the miniaturized SPR system was evaluated by the detection of immunoglobulin G (IgG).

Parametric optimization of visible wavelength gold lattice geometries for improved plasmon-enhanced fluorescence spectroscopy

We report the exploitation of spectroplasmonics for innovations in optical transducer development, specifically in the well-established application of labeled fluorescent analytes known as fluorescence spectroscopy. Presented herein are comprehensive analyses of nanoscale plasmonic lattice feature geometries using finite-difference time-domain software to determine the largest surface electric ($E$E) field enhancement resulting from localized surface plasmon resonance for reducing the limit of detection of plasmon-enhanced fluorescence. This parametric optimization of the critical dimensions of the plasmon resonance of noble metal nanostructures will enable improved excitation and emission enhancement of fluorophores used in visible wavelength fluorescence spectroscopy.

Advancements in SPR biosensing technology: An overview of recent trends in smart layers design, multiplexing concepts, continuous monitoring and in vivo sensing

Inspired by the rapid progress and existing limitations in surface plasmon resonance (SPR) biosensing technology, we have summarized the recent trends in the fields of both chip-SPR and fiber optic (FO)-SPR biosensors during the past five years, primarily regarding smart layers design, multiplexing, continuous monitoring and in vivo sensing. Versatile surface chemistries, biomaterials and nanomaterials have been utilized thus far to generate smart layers on SPR platforms and as such achieve oriented immobilization of bioreceptors, improved fouling resistance and sensitivity enhancement, collectively aiming to improve the biosensing performance. Furthermore, often driven by the desires for time- and cost-effective quantification of multiple targets in a single measurement, efforts have been made to implement multiplex bioassays on SPR platforms. While this aspect largely remains difficult to attain, numerous alternative strategies arose for obtaining parallel analysis of multiple analytes in one single device. Additionally, one of the upcoming challenges in this field will be to succeed in using SPR platforms for continuous measurements and in vivo sensing, and as such match up other biosensing platforms where these goals have been already conquered. Overall, this review will give insight into multiple possibilities that have become available over the years for boosting the performance of SPR biosensors. However, because combining them all into one optimal sensor is practically not feasible, the final application needs to be considered while designing an SPR biosensor, as this will determine the requirements of the bioassay and will thus help in selecting the essential elements from the recent progress made in SPR sensing.

Development of a Surface Plasmon Resonance and Fluorescence Imaging System for Biochemical Sensing

Surface plasmon resonance (SPR) biosensors are an extremely sensitive optical technique used to detect the changes in refractive index occurring at the sensor interface. Fluorescence involves the emission of light by a substance that has absorbed light or other electromagnetic radiation, and the parameters of the absorbed and emitted radiation are used to identify the presence and the amount of specific molecules in a specimen. SPR biosensors and fluorescence analysis are both effective methods for real-time detection. The combination of these technologies would improve the quantitative detection sensitivity of fluorescence analysis and the specificity of SPR detection. We designed and developed an SPR and fluorescence synchronous detection system. The SPR module was based on two kinds of modulation methods, and the fluorescence module was capable of switching between four wavelengths. The fluorescence microspheres and A549 cells of different concentration were both detected by the SPR and fluorescence method synchronously in real time. The fluorescent signal and the optical signal of the SPR were shown to correlate. The correlation coefficient for fluorescent microspheres detection reached up to 0.9866. The system could be used in cell analysis and molecule diagnosis in the future.

Advances in Surface Plasmon Resonance Imaging and Microscopy and Their Biological Applications

Surface plasmon resonance microscopy and imaging are optical methods that enable observation and quantification of interactions of nano- and microscale objects near a metal surface in a temporally and spatially resolved manner. This review describes the principles of surface plasmon resonance microscopy and imaging and discusses recent advances in these methods, in particular, in optical platforms and functional coatings. In addition, the biological applications of these methods are reviewed. These include the detection of a broad variety of analytes (nucleic acids, proteins, bacteria), the investigation of biological systems (bacteria and cells), and biomolecular interactions (drug-receptor, protein-protein, protein-DNA, protein-cell).

Recent Advances in Surface Plasmon Resonance Imaging Sensors

The surface plasmon resonance (SPR) sensor is an important tool widely used for studying binding kinetics between biomolecular species. The SPR approach offers unique advantages in light of its real-time and label-free sensing capabilities. Until now, nearly all established SPR instrumentation schemes are based on single- or several-channel configurations. With the emergence of drug screening and investigation of biomolecular interactions on a massive scale these days for finding more effective treatments of diseases, there is a growing demand for the development of high-throughput 2-D SPR sensor arrays based on imaging. The so-called SPR imaging (SPRi) approach has been explored intensively in recent years. This review aims to provide an up-to-date and concise summary of recent advances in SPRi. The specific focuses are on practical instrumentation designs and their respective biosensing applications in relation to molecular sensing, healthcare testing, and environmental screening.

Advances in nanoplasmonic biosensors for clinical applications

Plasmonic biosensors can be conveniently used as portable diagnostic devices for attaining timely and cost-effective clinical outcomes. Nanoplasmonics technology opens the way for sensor miniaturization, multiplexing and point of care testing.

Fabrication of carbohydrate microarrays on poly(2-hydroxyethyl methacrylate)-cyanuric chloride-modified substrates for the analysis of carbohydrate–lectin interactions

The pHEMA polymer provides an anti-fouling surface and the CC linker allows the covalent immobilization of intact carbohydrates.