Magnetic field-assisted SPR biosensor based on carboxyl-functionalized graphene oxide sensing film and Fe3O4-hollow gold nanohybrids probe

"Two-in-one" core-shell nanozyme probes with double signal amplification for high-performing surface plasmon resonance immunosensing

Herein, a "two-in-one" Ag@Au core-shell nanozyme probe inducing double-signal amplification has been developed to significantly elevate the sensitivity of SPR sensors via sandwich immunoassay. The Ag@Au core-shell nanozyme with intrinsic peroxide-like activity was demonstrated to catalyze a polymerization reaction leading to formation of polyaniline, allowing further improvement of detection performance of SPR immunosensor. The method demonstrated here offers a universal strategy for enhanced SPR detection and further expands the application of nanozymes.

A Novel SPR Immunosensor Based on Dual Signal Amplification Strategy for Detection of SARS-CoV-2 Nucleocapsid Protein

Since the global outbreak of coronavirus disease 2019 (COVID-19), it has spread rapidly around the world. The nucleocapsid (N) protein is one of the most abundant SARS-CoV-2 proteins. Therefore, a sensitive and effective detection method for SARS-CoV-2 N protein is the focus of research. Here, we developed a surface plasmon resonance (SPR) biosensor based on the dual signal-amplification strategy of Au@Ag@Au nanoparticles (NPs) and graphene oxide (GO). Additionally, a sandwich immunoassay was utilized to sensitively and efficiently detect SARS-CoV-2 N protein. On the one hand, Au@Ag@Au NPs have a high refractive index and the capability to electromagnetically couple with the plasma waves propagating on the surface of gold film, which are harnessed for amplifying the SPR response signal. On the other hand, GO, which has the large specific surface area and the abundant oxygen-containing functional groups, could provide unique light absorption bands that can enhance plasmonic coupling to further amplify the SPR response signal. The proposed biosensor could efficiently detect SARS-CoV-2 N protein for 15 min and the detection limit for SARS-CoV-2 N protein was 0.083 ng/mL, with a linear range of 0.1 ng/mL~1000 ng/mL. This novel method can meet the analytical requirements of artificial saliva simulated samples, and the developed biosensor had a good anti-interference capability.

Optical Biosensor Based on Graphene and Its Derivatives for Detecting Biomolecules

Graphene and its derivatives show great potential for biosensing due to their extraordinary optical, electrical and physical properties. In particular, graphene and its derivatives have excellent optical properties such as broadband and tunable absorption, fluorescence bursts, and strong polarization-related effects. Optical biosensors based on graphene and its derivatives make nondestructive detection of biomolecules possible. The focus of this paper is to review the preparation of graphene and its derivatives, as well as recent advances in optical biosensors based on graphene and its derivatives. The working principle of face plasmon resonance (SPR), surface-enhanced Raman spectroscopy (SERS), fluorescence resonance energy transfer (FRET) and colorimetric sensors are summarized, and the advantages and disadvantages of graphene and its derivatives applicable to various types of sensors are analyzed, and the methods of surface functionalization of graphene and its derivatives are introduced; these optical biosensors can be used for the detection of a range of biomolecules such as single cells, cellular secretions, proteins, nucleic acids, and antigen-antibodies; these new high-performance optical sensors are capable of detecting changes in surface structure and biomolecular interactions with the advantages of ultra-fast detection, high sensitivity, label-free, specific recognition, and the ability to respond in real-time. Problems in the current stage of application are discussed, as well as future prospects for graphene and its biosensors. Achieving the applicability, reusability and low cost of novel optical biosensors for a variety of complex environments and achieving scale-up production, which still faces serious challenges.

Research advances on surface plasmon resonance biosensors

The surface plasmon resonance (SPR) phenomenon is of wide interest due to its sensitivity to changes in surface refractive index for the label-free, highly sensitive and rapid detection of biomarkers. This paper reviews research progress on SPR biosensors modified with different substrate structures and surface materials, surface plasmon resonance imaging (SPRI), and SPR-enhanced electrochemiluminescent (ECL) biosensors for applications in biosensing in the last five years. This paper focuses on the research on the application of the SPR phenomenon in the field of bio-detection, reviews the sensing characteristics of SPR biosensors with substrate structures of prisms, gratings, and optical fibers, and summarizes and analyzes the sensitivity and interference resistance of SPR sensors with surface modification of different materials (high-refractive index dielectric films, metallic micro- and nanostructures, and surface antifouling materials). Considering that imaging is an important tool for biomedical detection, this paper reviews the research progress on SPRI technology in the field of biomedical detection. In addition, this paper also reviews the research progress on SPR-enhanced ECL biosensors in the field of biosensing. Finally, this paper provides an outlook on the development trends of biosensing technology in terms of portable high-precision SPR sensors, reduction of self-loss of thin film materials, optimization of image processing techniques and simplification of electrode modification for ECL sensors.

Novel nanostructure-coupled biosensor platform for one-step high-throughput quantification of serum neutralizing antibody after COVID-19 vaccination

COVID-19 vaccination efficacy depends on serum levels of the neutralizing antibodies (NAs) specific to the receptor-binding domain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Therefore, a high-throughput rapid assay capable of measuring the total SARS-CoV-2 NA level is urgently needed for COVID-19 serodiagnosis, convalescent plasma therapy, vaccine development, and assessment. Here, we developed a novel nanoplasmonic immunosorbent assay (NanoPISA) platform for one-step rapid quantification of SARS-CoV-2 NAs in clinical serum samples for high-throughput evaluation of COVID-19 vaccine effectiveness. The NanoPISA platform enhanced by the use of nanoporous hollow gold nanoparticle coupling was able to detect SARS-CoV-2 NAs with a limit of detection of 0.2 pM within 15 min without washing steps. The one-step NanoPISA for SARS-CoV-2 NA detection in clinical specimens yielded good results, comparable with those obtained in the gold-standard seroneutralization test and the surrogate virus-neutralizing enzyme-linked immunosorbent assay. Collectively, the one-step NanoPISA might be a rapid and high-throughput NA-quantification platform for evaluating the effectiveness of COVID-19 vaccines.

Double-Antibody Sandwich Immunoassay and Plasmonic Coupling Synergistically Improved Long-Range SPR Biosensor with Low Detection Limit

A long-range surface plasmonic resonance (LR-SPR) biosensor modified with double-antibody sandwich immunoassay and plasmonic coupling is demonstrated for human-immunoglobulin G detection with a low limit of detection (LOD). The double-antibody sandwich immunoassay dramatically changes the average refractive index of the medium layer on the sensor surface. The near-field electron coupling between the localized surface plasmon and the long-range surface plasmon leads to a significant perturbation of the evanescent field. The large penetration depth and the long propagation distance of the long-range surface plasmonic waves facilitate the LR-SPR sensor in the detection of biological macromolecules. The unique light absorption characteristic of the nanocomposite material in the sensor provides the in situ self-compensation for the disturbance. Therefore, besides the inherent advantages of optical fiber sensors, the developed biosensor can realize the detection of biomolecules with high sensitivity, low LOD and high accuracy and reliability. Experimental results demonstrate that the LOD of the biosensor is as low as 0.11 μg/mL in the detection of the phosphate-buffered saline sample, and the spike-and-repetition rate is 105.56% in the detection of the real serum sample, which partly shows the practicability of the biosensor. This indicates that the LR-SPR biosensor provides better response compared with existing similar sensors and can be regarded as a valuable method for biochemical analysis and disease detection.

Nanometer-Sized Boron Loaded Liposomes Containing Fe3O4 Magnetic Nanoparticles and Tributyl Borate and Anti-Albumin from Bovine Serum Antibody for Thermal Neutron Detection

A shortage in the supply of ³He used for thermal neutron detector makes researchers to find ³He alternatives for developing new neutron detectors. Here, we prepared a neutron-sensitive composite liposome with tributyl borate and encapsulating with Fe₃O₄@oleic acid nanoparticles (Fe₃O₄@OA NPs), methylene blue (MB), or anti-albumin from bovine serum (anti-BSA). The tributyl borate compound was characterized by Fourier transform infrared spectroscopy (FT-IR). In addition, the morphology, element compositions, and magnetic properties of the composite liposome were investigated with transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and vibrating sample magnetometer (VSM), respectively. The results indicated that a typical ellipsoidal magnetic liposome structure was obtained, and the lengths of the minor axis and major axis were 49 ± 1 nm and 87 ± 3 nm, respectively. Under thermal neutron irradiation, the structure of composite liposome was destroyed, and encapsulated reporter molecules were released, which was detected by ultraviolet–visible (UV–vis) spectroscopy and surface plasmon resonance (SPR) technology. The response of this sensor based on a destructive assay shows a good correlation with neutron doses. Besides, the sensor has a neutron to gamma-ray rejection ratio of 1568 at a thermal neutron flux rate of 135.6 n/cm²·s, which makes it a promising alternative to ³He.

One dimensional magneto-optical nanocomplex from silver nanoclusters and magnetite nanorods containing ordered mesocages for sensitive detection of PD-L1

Programmed death ligand 1 (PD-L1) is a typical immune checkpoint protein, whose up-regulation on the membrane of different tumor cells inhibits the immune response of T cells and leads to the escape of tumor cells. In this work, we designed a facile and highly specific surface plasmon resonance (SPR) biosensor to detect PD-L1 in human plasma based on magnetite nanorods containing ordered mesocages (MNOM) and silver nanoclusters (AgNCs). Magneto-optical nanocomplex MNOM@AgNCs with superior magneto-optical properties and high signal-to-noise ratio were fabricated to improve the detection sensitivity owing to the high specific surface area of MNOM and excellent localized SPR of AgNCs. The PD-L1 Antibody on the surface of gold chip and the PD-L1 aptamer on MNOM@AgNCs could realize dual selective recognition of PD-L1, providing the specificity of the sensor and reducing non-specific binding. The SPR sensor showed a good linear range of PD-L1 from 10 ng/mL to 300 ng/mL with the detection limit of 3.29 ng/mL. The practical performance of this immunosensing platform had been successfully verified by clinical samples which included healthy donors and cancer patients. Based on the analysis, the developed immunosensor provided a new strategy for point-of-care detection of PD-L1 and could be used as clinical companion diagnosis of PD-1/PD-L1 inhibitor therapy.

Biosensing platform on ferrite magnetic nanoparticles: Synthesis, functionalization, mechanism and applications

Ferrite magnetic nanoparticles (FMNPs) are gaining popularity to design biosensors for high-performance clinical diagnosis. The fusion of information shows that FMNPs based biosensors require well-tuned FMNPs as detection probes to produce large and specific biological signals with minimal non-specific binding. Nevertheless, there is a noticeable lacuna of information to solve the issues related to suitable synthesis route, particle size reduction, functionalization, sensitivity towards targeted intercellular biological tiny particles, and lower signal-to-noise ratio. Therefore it allows exploring unique characteristics of FMNPs to design a suitable sensing device for intracellular measurements and diseases detection. This review focuses on the extensively used synthesis routes, their advantages and limitations, crystalline structure, functionalization, along with recent applications of FMNPs in biosensors, taking into consideration their analytical figures of merit and range of linearity. This work also addresses the current progress, key factors for sensitivity, selectivity and productivity improvement along with the challenges, future trends and perspectives of FMNPs based biosensors.

Simultaneous detection of TNOS and P35S in transgenic soybean based on magnetic bicolor fluorescent probes

A magnetic-separation-dual-targets fluorescent biosensor was fabricated to detect terminator nopaline synthase (TNOS) and promoter of cauliflower mosaic virus 35s (P35S) in transgenic soybean based on incorporation of bicolor CdTe quantum dots carried by silica nanospheres. In this protocol, the fixed probes for TNOS or P35S were magnetized firstly with Fe3O4@Au magnetic nanosphere by Au-S covalent bonding to achieve magnetized probes. Meanwhile, the capture probes for TNOS or P35S were functionalized with green or red fluorescent microspheres respectively to obtain fluorescently-labeled probes, which could emit relative strong green or red fluorescent signal. Two terminals of TNOS or P35S were recognized by magnetized probes and fluorescently-labeled probes respectively to form the sandwiched structures in the process of biosensor development subsequently, and it was separated by a magnet instantly. The fluorescence intensities of remnant supernatant were measured and analyzed accordingly to achieve simultaneous detection of TNOS and P35S. This biosensor exhibited a good dynamic range, low limit of detection and excellent selectivity in detecting transgenic soybean.

Recent Progress in Optical Sensors for Biomedical Diagnostics

In recent years, several types of optical sensors have been probed for their aptitude in healthcare biosensing, making their applications in biomedical diagnostics a rapidly evolving subject. Optical sensors show versatility amongst different receptor types and even permit the integration of different detection mechanisms. Such conjugated sensing platforms facilitate the exploitation of their neoteric synergistic characteristics for sensor fabrication. This paper covers nearly 250 research articles since 2016 representing the emerging interest in rapid, reproducible and ultrasensitive assays in clinical analysis. Therefore, we present an elaborate review of biomedical diagnostics with the help of optical sensors working on varied principles such as surface plasmon resonance, localised surface plasmon resonance, evanescent wave fluorescence, bioluminescence and several others. These sensors are capable of investigating toxins, proteins, pathogens, disease biomarkers and whole cells in varied sensing media ranging from water to buffer to more complex environments such as serum, blood or urine. Hence, the recent trends discussed in this review hold enormous potential for the widespread use of optical sensors in early-stage disease prediction and point-of-care testing devices.

Optical-Based (Bio) Sensing Systems Using Magnetic Nanoparticles

In recent years, various reports related to sensing application research have suggested that combining the synergistic impacts of optical, electrical or magnetic properties in a single technique can lead to a new multitasking platform. Owing to their unique features of the magnetic moment, biocompatibility, ease of surface modification, chemical stability, high surface area, high mass transference, magnetic nanoparticles have found a wide range of applications in various fields, especially in sensing systems. The present review is comprehensive information about magnetic nanoparticles utilized in the optical sensing platform, broadly categorized into four types: surface plasmon resonance (SPR), surface-enhanced Raman spectroscopy (SERS), fluorescence spectroscopy and near-infrared spectroscopy and imaging (NIRS) that are commonly used in various (bio) analytical applications. The review also includes some conclusions on the state of the art in this field and future aspects.

Two-Dimensional Materials in Biosensing and Healthcare: From In Vitro Diagnostics to Optogenetics and Beyond

Since the isolation of graphene in 2004, there has been an exponentially growing number of reports on layered two-dimensional (2D) materials for applications ranging from protective coatings to biochemical sensing. Due to the exceptional, and often tunable, electrical, optical, electrochemical, and physical properties of these materials, they can serve as the active sensing element or a supporting substrate for diverse healthcare applications. In this review, we provide a survey of the recent reports on the applications of 2D materials in biosensing and other emerging healthcare areas, ranging from wearable technologies to optogenetics to neural interfacing. Specifically, this review provides (i) a holistic evaluation of relevant material properties across a wide range of 2D systems, (ii) a comparison of 2D material-based biosensors to the state-of-the-art, (iii) relevant material synthesis approaches specifically reported for healthcare applications, and (iv) the technological considerations to facilitate mass production and commercialization.

Low-fouling and highly sensitive fluorescence immunoassay of protein in serum based on the antifouling magnetic beads

Aim: A low-fouling and highly sensitive fluorescence immunoassay for protein detection in serum was proposed, and IgG was used as a model protein. Materials & methods: SH-PEG-NH2 serving as antifouling coating was conjugated with carboxyl Fe3O4 nanoparticles, and then, the thiol groups were conjugated with antibody via the covalent binding. IgG was captured through magnetic immunoreaction. Highly fluorescent quantum dots modified with streptavidin (SA-QDs) were united with biotin modified IgG antibody to form the sandwich structure. Results & conclusion: The fluorescence immunoassay was able to detect IgG with a detection limit of 3.89 ng/ml in buffer and 5.0 ng/ml in serum with satisfying selectivity and acceptable reproducibility, which demonstrated its potential application in quantitative analysis of real patient serum samples.

Superparamagnetic nanoarchitectures for disease-specific biomarker detection

Synthesis, bio-functionalization, and multifunctional activities of superparamagnetic-nanostructures have been extensively reviewed with a particular emphasis on their uses in a range of disease-specific biomarker detection and associated challenges.

A sensitive SPR biosensor based on hollow gold nanospheres and improved sandwich assay with PDA-Ag@Fe3O4/rGO

A novel surface plasmon resonance (SPR) biosensor based on hollow gold nanospheres (HGNPs) and an improved sandwich assay was developed to detect rabbit IgG. The electromagnetic coupling between the HGNPs and Au film, and the notable plasmonic fields spread over the inner and outer surfaces of HGNPs, led to the considerable amplification of the SPR signal. Polydopamine-Ag@Fe₃O₄/reduced graphene oxide (PDA-Ag@Fe₃O₄/rGO) was introduced to bind detection antibody (Ab₂) to form the improved sandwich structure. Ag nanoparticles were excited to produce SPR and their hot electrons were doped on graphene thin films, which amplified the response of biomolecules. Magnetic nanoparticles (Fe₃O₄) simplified the collection of Ab₂-PDA-Ag@Fe₃O₄/rGO. An external layer of polydopamine (PDA) permitted the efficient immobilization of Ab₂ without activation via abundant functional groups and protected the nanoparticles from etching or agglomeration. In addition, because of its large mass, Ab₂-PDA-Ag@Fe₃O₄/rGO also played a key role in the further amplification of the SPR response signals. This novel SPR biosensor exhibited an effective response to the rabbit IgG at the different concentrations ranging from 0.019 to 40.00μgmL^-1. This value is 132 times lower than that observed for a traditional SPR biosensor based on Au-3-mercaptopropionic acid and 8 times lower than that obtained from an Ab₂ sandwich assay, which indicates that the SPR sensor has high sensitivity. In addition, the designed biosensor showed satisfactory recoveries to detect the rabbit IgG spiked in serum samples. Therefore, the novel SPR biosensor with high sensitivity and acceptable recovery has potential for practical applications.