Noble Metal-Assisted Surface Plasmon Resonance Immunosensors

Size Effects of Gold Nanoparticles on Surface Plasmon Resonance Assays for DNA Hybridization

Recent advancements in signal amplifiers, such as biofunctionalized gold nanoparticles (AuNPs) have improved the surface plasmon resonance (SPR) performance. However, the correlation between the sizes of DNA-Au conjugates and the SPR chips remains elusive. We investigated how the size of AuNPs functioned with DNA detection probes (D-AuNPs) affect SPR signals in sandwich DNA hybridization assays. The effects of three sizes (5, 13, and 29 nm) of D-AuNPs with an equal surface probe density were systematically compared to delineate the relationship between signal amplification and steric hindrance. Sporadically adsorbed target DNA on sparse capture probe-coated chips led to a growth of signal amplification with larger D-AuNPs. In contrast, on dense capture probe-coated SPR chips, when the target DNA concentration was above 1.5 nM, the medium-sized 13 nm AuNPs displayed 1.7- and 1.3-fold enhancement factors than 5 nm and 29 nm ones, respectively. Our results indicate the steric hindrance disturbs the capture of D-AuNPs on dense target DNA-modified chips, rendering the surface density of captured D-AuNPs a determining factor of the sensor response. Alternatively, the sensor sensitivity to D-AuNP surface density is crucial on chips with sparse target DNA. These insights should stimulate and guide future research on surface functionalization toward SPR sensors and AuNPs.

Application and Method of Surface Plasmon Resonance Technology in the Preparation and Characterization of Biomedical Nanoparticle Materials

Surface Plasmon Resonance (SPR) technology, as a powerful analytical tool, plays a crucial role in the preparation, performance evaluation, and biomedical applications of nanoparticles due to its real-time, label-free, and highly sensitive detection capabilities. In the nanoparticle preparation process, SPR technology can monitor synthesis reactions and surface modifications in real-time, optimizing preparation techniques and conditions. SPR enables precise measurement of interactions between nanoparticles and biomolecules, including binding affinities and kinetic parameters, thereby assessing nanoparticle performance. In biomedical applications, SPR technology is extensively used in the study of drug delivery systems, biomarker detection for disease diagnosis, and nanoparticle-biomolecule interactions. This paper reviews the latest advancements in SPR technology for nanoparticle preparation, performance evaluation, and biomedical applications, discussing its advantages and challenges in biomedical applications, and forecasting future development directions.

Novel Au/Cu2NiSnS4 Nano-Heterostructure: Synthesis, Structure, Heterojunction Band Offset and Alignment, and Interfacial Charge Transfer Dynamics

Considering the importance of physics and chemistry at material interfaces, we have explored the coupling of multinary chalcogenide semiconductor Cu2NiSnS4 nanoparticles (CNTS NPs) for the first time with the noble metal (Au) to form Au-CNTS nano-heterostructures (NHSs). The Au-CNTS NHSs is synthesized by a simple facile hot injection method. Synergistic experimental and theoretical approaches are employed to characterize the structural, optical, and electrical properties of the Au-CNTS NHSs. The absorption spectra demonstrate enhanced and broadened optical absorption in the ultraviolet-visible-near-infrared (UV-Vis-NIR) region, which is corroborated by cyclic voltammetry (CV) readings. CV measurements show type II staggered band alignment, with a conduction band offset (CBO) of 0.21 and 0.23 eV at the Au-CNTS/CdS and CNTS/CdS interface, respectively. Complementary first-principles density functional theory (DFT) calculations predict the formation of a stable Au-CNTS NHSs, with the Au nanoparticle transferring its electrons to the CNTS. Moreover, our interface analysis using ultrafast transient absorption experiments demonstrate that the Au-CNTS NHSs facilitates efficient transport and separation of photoexcited charge carriers when compared to pristine CNTS. The transient measurements further reveal a plasmonic electronic transfer from the Au nanoparticle to CNTS. Our advanced analysis and findings will prompt investigations into new functional materials and their photo/electrocatalysis and optoelectronic device applications in the future.

Efficient Sequential Detection of Two Antibiotics Using a Fiber-Optic Surface Plasmon Resonance Sensor

Antibiotic residues have become a worldwide public safety issue. It is vital to detect multiple antibiotics simultaneously using sensors. A new and efficient method is proposed for the combined detection of two antibiotics (enrofloxacin (Enro) and ciprofloxacin (Cip)) in milk using surface plasmon resonance (SPR) sensors. Based on the principle of immunosuppression, two antibiotic antigens (for Enro and Cip) were immobilized on an optical fiber surface with conjugates of bovine serum albumin using dopamine (DA) polymerization. Each single antigen was bound to its corresponding antibody to derive standard curves for Enro and Cip. The fiber-optic sensor's sensitivity was 2900 nm/RIU. Detection limits were calculated to be 1.20 ng/mL for Enro and 0.81 ng/mL for Cip. The actual system's recovery rate was obtained by testing Enro and Cip in milk samples; enrofloxacin's and ciprofloxacin's mean recoveries from the milk samples were 96.46-120.46% and 96.74-126.9%, respectively. In addition, several different regeneration solutions were tested to analyze the two target analytes' regeneration ability; NaOH and Gly-HCl solutions were found to have the best regeneration ability.

Plasmonic Nanoparticle-Enhanced Optical Techniques for Cancer Biomarker Sensing

This review summarizes recent advances in leveraging localized surface plasmon resonance (LSPR) nanotechnology for sensitive cancer biomarker detection. LSPR arising from noble metal nanoparticles under light excitation enables the enhancement of various optical techniques, including surface-enhanced Raman spectroscopy (SERS), dark-field microscopy (DFM), photothermal imaging, and photoacoustic imaging. Nanoparticle engineering strategies are discussed to optimize LSPR for maximum signal amplification. SERS utilizes electromagnetic enhancement from plasmonic nanostructures to boost inherently weak Raman signals, enabling single-molecule sensitivity for detecting proteins, nucleic acids, and exosomes. DFM visualizes LSPR nanoparticles based on scattered light color, allowing for the ultrasensitive detection of cancer cells, microRNAs, and proteins. Photothermal imaging employs LSPR nanoparticles as contrast agents that convert light to heat, producing thermal images that highlight cancerous tissues. Photoacoustic imaging detects ultrasonic waves generated by LSPR nanoparticle photothermal expansion for deep-tissue imaging. The multiplexing capabilities of LSPR techniques and integration with microfluidics and point-of-care devices are reviewed. Remaining challenges, such as toxicity, standardization, and clinical sample analysis, are examined. Overall, LSPR nanotechnology shows tremendous potential for advancing cancer screening, diagnosis, and treatment monitoring through the integration of nanoparticle engineering, optical techniques, and microscale device platforms.

SARS-CoV-2 Virus-like Particles with Plasmonic Au Cores and S1-Spike Protein Coronas

The COVID-19 pandemic has stimulated the scientific world to intensify virus-related studies aimed at the development of quick and safe ways of detecting viruses in the human body, studying the virus-antibody and virus-cell interactions, and designing nanocarriers for targeted antiviral therapies. However, research on dangerous viruses can only be performed in certified laboratories that follow strict safety procedures. Thus, developing deactivated virus constructs or safe-to-use virus-like objects, which imitate real viruses and allow performing virus-related studies in any research laboratory, constitutes an important scientific challenge. Such species, called virus-like particles (VLPs), contain instead of capsids with viral DNA/RNA empty or synthetic cores with real virus proteins attached to them. We have developed a method for the preparation of VLPs imitating the virus responsible for the COVID-19 disease: the SARS-CoV-2. The particles have Au cores surrounded by "coronas" of S1 domains of the virus's spike protein. Importantly, they are safe to use and specifically interact with SARS-CoV-2 antibodies. Moreover, Au cores exhibit localized surface plasmon resonance (LSPR), which makes the synthesized VLPs suitable for biosensing applications. During the studies, the effect allowed us to visualize the interaction between the VLPs and the antibodies and identify the characteristic vibrational signals. What is more, additional functionalization of the particles with a fluorescent label revealed their potential in studying specific virus-related interactions. Notably, the universal character of the developed synthesis method makes it potentially applicable for fabricating VLPs imitating other life-threatening viruses.

Recent Development in Plasmonic Nanobiosensors for Viral DNA/RNA Biomarkers

Recently, due to the coronavirus pandemic, the need for early diagnosis of infectious diseases, including viruses, is emerging. Though early diagnosis is essential to prevent infection and progression to severe illness, there are few technologies that accurately measure low concentrations of biomarkers. Plasmonic nanomaterials are attracting materials that can effectively amplify various signals, including fluorescence, Raman, and other optical and electromagnetic output. In this review, we introduce recently developed plasmonic nanobiosensors for measuring viral DNA/RNA as potential biomarkers of viral diseases. In addition, we discuss the future perspective of plasmonic nanobiosensors for DNA/RNA detection. This review is expected to help the early diagnosis and pathological interpretation of viruses and other diseases.

Direct detection of virus-like particles using color images of plasmonic nanostructures

We propose a measurement method for sensitive and label-free detections of virus-like particles (VLPs) using color images of nanoplasmonic sensing chips. The nanoplasmonic chip consists of 5×5 gold nanoslit arrays and the gold surface is modified with specific antibodies for spike protein. The resonant wavelength of the 430-nm-period gold nanoslit arrays underwater environment is about 570 nm which falls between the green and red bands of the color CCD. The captured VLPs by the specific antibodies shift the plasmonic resonance of the gold nanoslits. It results in an increased brightness of green pixels and decreased brightness of red pixels. The image contrast signals of (green - red) / (red + green) show good linearity with the surface particle density. The experimental tests show the image contrast method can detect 100-nm polystyrene particles with a surface density smaller than 2 particles/µm². We demonstrate the application for direct detection of SARS-CoV-2 VLPs using a simple scanner platform. A detection limit smaller than 1 pg/mL with a detection time less than 30 minutes can be achieved.

Bi-ECDAQ: An electrochemical dual-immuno-biosensor accompanied by a customized bi-potentiostat for clinical detection of SARS-CoV-2 Nucleocapsid proteins

Multiplex electrochemical biosensors have been used for eliminating the matrix effect in complex bodily fluids or enabling the detection of two or more bioanalytes, overall resulting in more sensitive assays and accurate diagnostics. Many electrochemical biosensors lack reliable and low-cost multiplexing to meet the requirements of point-of-care detection due to either limited functional biosensors for multi-electrode detection or incompatible readout systems. We developed a new dual electrochemical biosensing unit accompanied by a customized potentiostat to address the unmet need for point-of-care multi-electrode electrochemical biosensing. The two-working electrode system was developed using screen-printing of a carboxyl-rich nanomaterial containing ink, with both working electrodes offering active sites for recognition of bioanalytes. The low-cost bi-potentiostat system (∼$80) was developed and customized specifically to the bi-electrode design and used for rapid, repeatable, and accurate measurement of electrochemical impedance spectroscopy signals from the dual biosensor. This binary electrochemical data acquisition (Bi-ECDAQ) system accurately and selectively detected SARS-CoV-2 Nucleocapsid protein (N-protein) in both spiked samples and clinical nasopharyngeal swab samples of COVID-19 patients within 30 min. The two working electrodes offered the limit of detection of 116 fg/mL and 150 fg/mL, respectively, with the dynamic detection range of 1-10,000 pg/mL and the sensitivity range of 2744-2936 Ω mL/pg.mm2 for the detection of N-protein. The potentiostat performed comparable or better than commercial Autolab potentiostats while it is significantly lower cost. The open-source Bi-ECDAQ presents a customizable and flexible approach towards addressing the need for rapid and accurate point-of-care electrochemical biosensors for the rapid detection of various diseases.

Advanced Nanomaterials for Preparedness Against (Re-)Emerging Viral Diseases

While the coronavirus disease (COVID-19) accounts for the current global pandemic, the emergence of other unknown pathogens, named "Disease X," remains a serious concern in the future. Emerging or re-emerging pathogens continue to pose significant challenges to global public health. In response, the scientific community has been urged to create advanced platform technologies to meet the ever-increasing needs presented by these devastating diseases with pandemic potential. This review aims to bring new insights to allow for the application of advanced nanomaterials in future diagnostics, vaccines, and antiviral therapies, thereby addressing the challenges associated with the current preparedness strategies in clinical settings against viruses. The application of nanomaterials has advanced medicine and provided cutting-edge solutions for unmet needs. Herein, an overview of the currently available nanotechnologies is presented, highlighting the significant features that enable them to control infectious diseases, and identifying the challenges that remain to be addressed for the commercial production of nano-based products is presented. Finally, to conclude, the development of a nanomaterial-based system using a "One Health" approach is suggested. This strategy would require a transdisciplinary collaboration and communication between all stakeholders throughout the entire process spanning across research and development, as well as the preclinical, clinical, and manufacturing phases.

SP, N. M, Barik AK, Pai KM, Unnikrishnan VK, George SD, Kartha VB, Chidangil S. Photonics of human saliva: potential optical methods for the screening of abnormal health conditions and infections

Human saliva can be treated as a pool of biological markers able to reflect on the state of personal health. Recent years have witnessed an increase in the use of optical devices for the analysis of body fluids. Several groups have carried out studies investigating the potential of saliva as a non-invasive and reliable clinical specimen for use in medical diagnostics. This brief review aims to highlight the optical technologies, mainly surface plasmon resonance (SPR), Raman, and Fourier transform infrared (FTIR) spectroscopy, which are being used for the probing of saliva for diverse biomedical applications. Advances in bio photonics offer the promise of unambiguous, objective and fast detection of abnormal health conditions and viral infections (such as COVID-19) from the analysis of saliva.

Recent Advancements in Receptor Layer Engineering for Applications in SPR-Based Immunodiagnostics

The rapid progress in the development of surface plasmon resonance-based immunosensing platforms offers wide application possibilities in medical diagnostics as a label-free alternative to enzyme immunoassays. The early diagnosis of diseases or metabolic changes through the detection of biomarkers in body fluids requires methods characterized by a very good sensitivity and selectivity. In the case of the SPR technique, as well as other surface-sensitive detection strategies, the quality of the transducer-immunoreceptor interphase is crucial for maintaining the analytical reliability of an assay. In this work, an overview of general approaches to the design of functional SPR-immunoassays is presented. It covers both immunosensors, the design of which utilizes well-known and often commercially available substrates, as well as the latest solutions developed in-house. Various approaches employing chemical and passive binding, affinity-based antibody immobilization, and the introduction of nanomaterial-based surfaces are discussed. The essence of their influence on the improvement of the main analytical parameters of a given immunosensor is explained. Particular attention is paid to solutions compatible with the latest trends in the development of label-free immunosensors, such as platforms dedicated to real-time monitoring in a quasi-continuous mode, the use of in situ-generated receptor layers (elimination of the regeneration step), and biosensors using recombinant and labelled protein receptors.

Detection of pathogenic bacteria by magneto-immunoassays: a review

Magnetic particle-based immunoassays are widely used in microbiology-related assays for both microbial capture, separation, analysis, and detection. Besides facilitating sample operation, the implementation of micro-to-nanometer scale magnetic beads as a solid support potentially shortens the incubation time (for magnetic immuno capture) from several hours to less than an hour. Analytical technologies based on magnetic beads offer a rapid, effective and inexpensive way to separate and concentrate the target analytes prior to detection. Magneto-immuno separation uses magnetic particles coated with specific antibodies to capture target microorganisms, bear the corresponding antigens, and subsequently separate them from the sample matrix in a magnetic field. The method has been proven effective in separating various types of pathogenic bacteria from environmental water samples and in eliminating background interferences. Magnetic particles are often used to capture target cells (pathogenic bacteria) from samples. In most commercially available assays, the actual identification and quantitation of the captured cells is then performed by classical microbiological assays. This review highlights the most sensitive analytic methods (i.e., long-range surface plasmon resonance and electrochemical impedance spectroscopy) to detect magnetically tagged bacteria in conjunction with magnetic actuation.

Magnetic nanoparticle-based amplification of microRNA detection in body fluids for early disease diagnosis

Circulating biomarkers such as microRNAs (miRNAs), short noncoding RNA strands, represent prognostic and diagnostic indicators for a variety of physiological disorders making their detection and quantification an attractive approach for minimally invasive early disease diagnosis. However, highly sensitive and selective detection methods are required given the generally low abundance of miRNAs in body fluids together with the presence of large amounts of other potentially interfering biomolecules. Although a variety of miRNA isolation and detection methods have been established in clinics, they usually require trained personnel and often constitute labor-, time- and cost-intensive approaches. During the last years, nanoparticle-based biosensors have received increasing attention due to their superior detection efficiency even in very low concentration regimes. This is based on their unique physicochemical properties in combination with their high surface area that allows for the immobilization of multiple recognition sites resulting in fast and effective recognition of analytes. Among various materials, magnetic nanoparticles have been identified as useful tools for the separation, concentration, and detection of miRNAs. Here, we review state-of-the-art technology with regard to magnetic particle-based miRNA detection from body fluids, critically discussing challenges and future perspective of such biosensors while comparing their handling, sensitivity as well as selectivity against the established miRNA isolation and detection methods.

Gold Nano-Island Platforms for Localized Surface Plasmon Resonance Sensing: A Short Review

Nano-islands are entities (droplets or other shapes) that are formed by spontaneous dewetting (agglomeration, in the early literature) of thin and very thin metallic (especially gold) films on a substrate, done by post-deposition heating or by using other sources of energy. In addition to thermally generated nano-islands, more recently, nanoparticle films have also been dewetted, in order to form nano-islands. The localized surface plasmon resonance (LSPR) band of gold nano-islands was found to be sensitive to changes in the surrounding environment, making it a suitable platform for sensing and biosensing applications. In this review, we revisit the development of the concept of nano-island(s), the thermodynamics of dewetting of thin metal films, and the effect of the substrate on the morphology and optical properties of nano-islands. A special emphasis is made on nanoparticle films and their applications to biosensing, with ample examples from the authors’ work.

Recent Progress in Plasmonic Biosensing Schemes for Virus Detection

The global burden of coronavirus disease 2019 (COVID-19) to public health and global economy has stressed the need for rapid and simple diagnostic methods. From this perspective, plasmonic-based biosensing can manage the threat of infectious diseases by providing timely virus monitoring. In recent years, many plasmonics’ platforms have embraced the challenge of offering on-site strategies to complement traditional diagnostic methods relying on the polymerase chain reaction (PCR) and enzyme-linked immunosorbent assays (ELISA). This review compiled recent progress on the development of novel plasmonic sensing schemes for the effective control of virus-related diseases. A special focus was set on the utilization of plasmonic nanostructures in combination with other detection formats involving colorimetric, fluorescence, luminescence, or Raman scattering enhancement. The quantification of different viruses (e.g., hepatitis virus, influenza virus, norovirus, dengue virus, Ebola virus, Zika virus) with particular attention to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was reviewed from the perspective of the biomarker and the biological receptor immobilized on the sensor chip. Technological limitations including selectivity, stability, and monitoring in biological matrices were also reviewed for different plasmonic-sensing approaches.