Ultra-sensitive detection by metal nanoparticles-mediated enhanced SPR biosensors

Recent advances in surface plasmon resonance for the detection of ovarian cancer biomarkers: a thorough review

Early detection of ovarian cancer (OC) is crucial for effective management and treatment, as well as reducing mortality rates. However, the current diagnostic methods for OC are time-consuming and have low accuracy. Surface plasmon resonance (SPR) biosensors offer a promising alternative to conventional techniques, as they enable rapid and less invasive screening of various circulating indicators. These biosensors are widely used for biomolecular interaction analysis and detecting tumor markers, and they are currently being investigated as a rapid diagnostic tool for early-stage cancer detection. Our main focus is on the fundamental concepts and performance characteristics of SPR biosensors. We also discuss the latest advancements in SPR biosensors that enhance their sensitivity and enable high-throughput quantification of OC biomarkers, including CA125, HE4, CEA, and CA19-9. Finally, we address the future challenges that need to be overcome to advance SPR biosensors from research to clinical applications. The ultimate goal is to facilitate the translation of SPR biosensors into routine clinical practice for the early detection and management of OC.

Beetle-inspired AuNPs semi-embedded colloidal crystal chips for the highly sensitive and colored detection of chloramphenicol in foods

Inspired by the desert beetle, a novel biomimetic chip was developed to detect chloramphenicol (CP). The chip was characterized by a periodic array in which hydrophobic Au nanoparticles (AuNPs) were semi-embedded on hydrophilic polymethyl methacrylate (PMMA) spheres. Among them, the AuNPs exhibited both a localized surface plasmon resonance effect to amplify the reflected signal and a synergistic effect with PMMA spheres to create a significant hydrophilic-hydrophobic interface, which facilitated the enrichment of target CP molecules and improved sensitivity. After optimization, the chip showed direct, ultrasensitive (as low as 0.2 ng/mL), fast (5 min), and selective detection of CP with a wide concentration range extending from 0.2 ng/mL to 1000 ng/mL. During detection, color changes of the chip were observed by naked eyes without any color display equipment. The recovery of CP was between 94.65 % and 108.70 % in chicken and milk samples.

An overview of signal amplification strategies and construction methods on phage-based biosensors

Phages are a class of viruses that specifically infect host bacteria. Compared to other recognition elements, phages offer several advantages such as high specificity, easy to obtain and good environmental tolerance, etc. These advantages underscore the potential of phages as recognition elements in the construction of biosensors. Therefore, the phage-based biosensors are currently garnering widespread attention for detecting pathogens in recent years. However, the test performance such as detection limit, sensitivity and stability of exicting phage-based biosensors require enhancement. In the design of sensors, the selection of various materials and construction methods significantly influences the test performance of the sensor, and employing appropriate signal amplification strategies and construction methods to devise biosensors based on different principles is an effective strategy to enhance sensor performance. The manuscript primarily focuses on the signal amplification strategies and construction methods employed in phage-based biosensors recent ten years, and summarizes the advantages and disadvantages of different signal amplification strategies and construction methods. Meanwhile, the manuscript discusses the relationship between sensor performance and various materials and construction methods, and reviews the application progress of phage-based electrochemical biosensors in the detection of foodborne bacteria. Furthermore, the manuscript points out the present limitations and the future research direction for the field of phage-based biosensors, so as to provide the reference for developing high-performance phage-based biosensors.

Applications of Metals and Metal Compounds in Improving the Sensitivity of Microfluidic Biosensors - A Review

The enhancement of detection sensitivity in microfluidic sensors has been a continuously explored field. Initially, many strategies for sensitivity improvement involved introducing enzyme cascade reactions, but enzyme-based reactions posed challenges in terms of cost, stability, and storage. Therefore, there is an urgent need to explore enzyme-free cascade amplification methods, which are crucial for expanding the application range and improving detection stability. Metal or metal compound nanomaterials have gained great attention in the exploitation of microfluidic sensors due to their ease of preparation, storage, and lower cost. The unique physical properties of metallic nanomaterials, including surface plasmon resonance, surface-enhanced Raman scattering, metal-enhanced fluorescence, and surface-enhanced infrared absorption, contribute significantly to enhancing detection capabilities. The metal-based catalytic nanomaterials, exemplified by Fe3O4 nanoparticles and metal-organic frameworks, are considered viable alternatives to biological enzymes due to their excellent performance. Herein, we provide a detailed overview of the applications of metals and metal compounds in improving the sensitivity of microfluidic biosensors. This review not only highlights the current developments but also critically analyzes the challenges encountered in this field. Furthermore, it outlines potential directions for future research, contributing to the ongoing development of microfluidic biosensors with improved detection 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.

Gold nanoparticles-based biosensors: pioneering solutions for bacterial and viral pathogen detection-a comprehensive review

Gold Nanoparticles (AuNPs) have gained significant attention in biosensor development due to their unique physical, chemical, and optical properties. When incorporated into biosensors, AuNPs offer several advantages, including a high surface area-to-volume ratio, excellent biocompatibility, ease of functionalization, and tunable optical properties. These properties make them ideal for the detection of various biomolecules, including proteins, nucleic acids, and bacterial and viral biomarkers. Traditional methods for detecting bacteria and viruses, such as RT-PCR and ELISA, often suffer from complexities, time consumption, and labor intensiveness. Consequently, researchers are continuously exploring novel devices to address these limitations and effectively detect a diverse array of infectious pathogenic microorganisms. In light of these challenges, nanotechnology has been instrumental in refining the architecture and performance of biosensors. By leveraging advancements in nanomaterials and strategies of biosensor fabrication the sensitivity and specificity of biosensors can be enhanced, enabling more precise detection of pathogenic bacteria and viruses. This review explores the versatility of AuNPs in detecting a variety of biomolecules, including proteins, nucleic acids, and bacterial and viral biomarkers. Furthermore, it evaluates recent advancements in AuNPs-based biosensors for the detection of pathogens, utilizing techniques such as optical biosensors, lateral flow immunoassays, colorimetric immunosensors, electrochemical biosensors, and fluorescence nanobiosensors. Additionally, the study discusses the existing challenges in the field and proposes future directions to improve AuNPs-based biosensors, with a focus on enhancing sensitivity, selectivity, and their utility in clinical and diagnostic applications.

Ultrasensitive Quantification of MUC16 Antigen/Amine-Terminated Aptamer Interaction by Surface Plasmon Resonance: Kinetic and Thermodynamic Studies

Purpose

MUC16 is a commonly employed biomarker to identify and predict ovarian cancer (OC). Precise measurement of MUC16 levels is essential for the accurate diagnosis, prediction, and management of OC. This research seeks to introduce a new surface plasmon resonance (SPR) biosensor design that utilizes aptamer-based technology to enable the sensitive and real-time detection of MUC16.

Methods

In this study, the sensor chip was immobilized with an anti-MUC16 aptamer (Ap) by utilizing 11-mercaptoundecanoic acid (MUA) as a linker to attach the amine-terminated Ap to the chip using EDC/NHS chemistry.

Results

The results indicated that the newly created aptasensor had a detection limit of 0.03 U/mL for MUC16 concentration, with a linear range of 0.09 to 0.27 U/mL. The findings demonstrate good precision and accuracy (<15%) for each MUC16 concentration, with recoveries ranging from 93% to 96%. Additionally, the aptasensor exhibited high selectivity, good repeatability, stability, and applicability in real human serum samples, indicating its potential as a valuable tool for the diagnosis and treatment of OC.

Conclusion

According to the outcomes, the designed aptasensor exhibited acceptable specificity to detect the CA125 antigen and could be utilized for the serum detection of target antigen by SPR method.

Revolutionizing agriculture with nanotechnology: Innovative approaches in fungal disease management and plant health monitoring

Nanotechnology has emerged as a transformative force in modern agriculture, offering innovative solutions to address challenges related to fungal plant diseases and overall agricultural productivity. Specifically, the antifungal activities of metal, metal oxide, bio-nanoparticles, and polymer nanoparticles were examined, highlighting their unique mechanisms of action against fungal pathogens. Nanoparticles can be used as carriers for fungicides, offering advantages in controlled release, targeted delivery, and reduced environmental toxicity. Nano-pesticides and nano-fertilizers can enhance nutrient uptake, plant health, and disease resistance were explored. The development of nanosensors, especially those utilizing quantum dots and plasmonic nanoparticles, promises early and accurate detection of fungal pathogens, a crucial step in timely disease management. However, concerns about their potential toxic effects on non-target organisms, environmental impacts, and regulatory hurdles underscore the importance of rigorous research and impact assessments. The review concludes by emphasizing the significant prospects of nanotechnology in reshaping the future of agriculture but advocates for a balanced approach that prioritizes safety, sustainability, and environmental stewardship.

DNAzyme amplified dispersion state change of gold nanoparticles and its dual optical channels for ultrasensitive and facile detection of lead ion in preserved eggs

A dual-mode sensing platform for Pb2+ was constructed based on the dual optical channels of Au NPs system with the amplification of DNAzyme, and it was successfully applied for Pb2+ determination in preserved egg with satisfactory results. The presence of Pb2+ activated the DNAzyme and induced the dispersion change of Au NPs in high salt concentration. The sequent absorption change of Au NPs was translated to the fluorescence change of carbon dots through FRET, and the scattering change was transferred to grey value of images involving the Tyndall effect. Thus, a sensing platform based on fluorescence and colorimetric dual-technique was achieved for Pb2+ detection, under the optimized conditions. With the assistance of DNAzyme, the linear range of fluorometric and colorimetric method were 2.0 × 10-14 ∼ 8.0 × 10-10 mol/L and 2.4 × 10-13 ∼ 9.5 × 10-9 mol/L, respectively. The dual-mode sensing platform demonstrated its promising application in the environmental monitoring and food safety field.

Simultaneous detection method for two cardiac disease protein biomarkers on a single chip modified with mixed aptamers using surface plasmon resonance

A simultaneous detection method for two cardiac disease protein biomarkers present in serum samples on a single planar gold chip using surface plasmon resonance (SPR) is described. The detection of N-terminal pro-brain natriuretic peptide (NT-proBNP) and tumor necrosis factor α (TNF-α), which are known as acute myocardial infarction (AMI) biomarkers, with predetermined clinically relevant concentrations was performed using mixed aptamers specific to each protein tethered on a single gold surface. After the binding of NT-proBNP and/or TNF-α to the mixed aptamers, an antibody specific to each target protein was injected to form a surface sandwich complex to improve selectivity. In order to adjust the dynamic ranges in the known clinically relevant concentration significantly different for NT-proBNP (0.13-0.24 nM) and TNF-α (0.5-3 pM), the surface density ratios of the corresponding pair of aptamer and antibody were first systematically determined, which were the 1:1 mixed aptamer chip with 40 nM anti-NT-proBNP and 100 nM anti-TNF-α. This allowed to establish the distinct dynamic ranges of 0.05-0.5 nM for NT-proBNP and 0.1-5 pM for TNF-α in a buffer, along with detection and quantification limits of 0.03 and 0.19 nM for NT-proBNP and 0.06 and 0.21 pM for TNF-α, respectively. The changes in refractive unit (RU) values observed when exposing both proteins at different concentrations alongside the corresponding fixed concentration of antibodies onto the 1:1 mixed aptamer chip were then correlated to the sum of RU values measured when using the injection of individual protein for evaluating each protein concentration. With a complete characterization of the simultaneous quantification of two protein concentrations in the buffer, the mixed aptamer chip was finally employed for direct measurements of NT-proBNP and TNF-α concentrations in undiluted serum samples from healthy controls and AMI patients. The results of simultaneous SPR measurements for the two proteins in the serum samples were further compared to the individual protein concentration results using an enzyme-linked immunosorbent assay.

A Point-of-Care Testing Device Utilizing Graphene-Enhanced Fiber Optic SPR Sensor for Real-Time Detection of Infectious Pathogens

Timely detection of highly infectious pathogens is essential for preventing and controlling public health risks. However, most traditional testing instruments require multiple tedious steps and ultimately testing in hospitals and third-party laboratories. The sample transfer process significantly prolongs the time to obtain test results. To tackle this aspect, a portable fiber optic surface plasmon resonance (FO-SPR) device was developed for the real-time detection of infectious pathogens. The portable device innovatively integrated a compact FO-SPR sensing component, a signal acquisition and processing system, and an embedded power supply unit. A gold-plated fiber is used as the FO-SPR sensing probe. Compared with traditional SPR sensing systems, the device is smaller size, lighter weight, and higher convenience. To enhance the detection capacity of pathogens, a monolayer graphene was coated on the sensing region of the FO-SPR sensing probe. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was used to evaluate the performance of the portable device. The device can accurately detect the SARS-CoV-2 spike S1 protein in phosphate-buffered saline (PBS) and artificial saliva within just 20 min, and the device successfully detected cultured SARS-CoV-2 virus. Furthermore, the FO-SPR probe has long-term stability, remaining stable for up to 8 days. It could distinguish between the SARS-CoV-2 spike protein and the MERS-CoV spike protein. Hence, this FO-SPR device provides reliable, rapid, and portable access to test results. It provides a promising point-of-care testing (POCT) tool for on-site screening of infectious pathogens.

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.

Development of a Gold Nanoparticle-Linked Immunosorbent Assay of Staphylococcal Enterotoxin B Detection with Extremely High Sensitivity by Determination of Gold Atom Content Using Graphite Furnace Atomic Absorption Spectrometry

Highly sensitive staphylococcal enterotoxin B (SEB) assay is of great importance for the prevention of toxic diseases caused by SEB. In this study, we present a gold nanoparticle (AuNP)-linked immunosorbent assay (ALISA) for detecting SEB in a sandwich format using a pair of SEB specific monoclonal antibodies (mAbs) performed in microplates. First, the detection mAb was labeled with AuNPs of different particle sizes (15, 40 and 60 nm). Then the sandwich immunosorbent assay for SEB detection was performed routinely in a microplate except for using AuNPs-labeled detection mAb. Next, the AuNPs adsorbed on the microplate were dissolved with aqua regia and the content of gold atoms was determined by graphite furnace atomic absorption spectrometry (GFAAS). Finally, a standard curve was drawn of the gold atomic content against the corresponding SEB concentration. The detection time of ALISA was about 2.5 h. AuNPs at 60 nm showed the highest sensitivity with an actual measured limit of detection (LOD) of 0.125 pg/mL and a dynamic range of 0.125-32 pg/mL. AuNPs at 40 nm had an actual measured LOD of 0.5 pg/mL and a dynamic range of 0.5 to 128 pg/mL. AuNPs at 15 nm had an actual measured LOD of 5 pg/mL, with a dynamic range of 5-1280 pg/mL. With detection mAb labeled with AuNPs at 60 nm, ALISA's intra- and interassay coefficient variations (CV) at three concentrations (2, 8, and 20 pg/mL) were all lower than 12% and the average recovery level was ranged from 92.7% to 95.0%, indicating a high precision and accuracy of the ALISA method. Moreover, the ALISA method could be successfully applied to the detection of various food, environmental, and biological samples. Therefore, the successful establishment of the ALISA method for SEB detection might provide a powerful tool for food hygiene supervision, environmental management, and anti-terrorism procedures and this method might achieve detection and high-throughput analysis automatically in the near future, even though GFAAS testing remains costly at present.

Advanced nanoscale drug delivery systems for bone cancer therapy

Bone tumors are relatively rare, which are complex cancers and mostly involve the long bones and pelvis. Bone cancer is mainly categorized into osteosarcoma (OS), chondrosarcoma, and Ewing sarcoma. Of these, OS is the most intimidating cancer of the bone tissue, which is mostly found in the log bones in young children and older adults. Conspicuously, the current chemotherapy modalities used for the treatment of OS often fail mainly due to (i) the non-specific detrimental effects on normal healthy cells/tissues, (ii) the possible emergence of drug resistance mechanisms by cancer cells, and (iii) difficulty in the efficient delivery of anticancer drugs to the target cells. To impose the maximal therapeutic impacts on cancerous cells, it is of paramount necessity to specifically deliver chemotherapeutic agents to the tumor site and target the diseased cells using advanced nanoscale multifunctional drug delivery systems (DDSs) developed using organic and inorganic nanosystems. In this review, we provide deep insights into the development of various DDSs applied in targeting and eradicating OS. We elaborate on different DDSs developed using biomaterials, including chitosan, collagen, poly(lactic acid), poly(lactic-co-glycolic acid), polycaprolactone, poly(ethylene glycol), polyvinyl alcohol, polyethyleneimine, quantum dots, polypeptide, lipid NPs, and exosomes. We also discuss DDSs established using inorganic nanoscale materials such as magnetic NPs, gold, zinc, titanium NPs, ceramic materials, silica, silver NPs, and platinum NPs. We further highlight anticancer drugs' role in bone cancer therapy and the biocompatibility of nanocarriers for OS treatment.

Inversion of the Complex Refractive Index of Au-Ag Alloy Nanospheres Based on the Contour Intersection Method

The contour intersection method is a new method used to invert the complex refractive index of small particles. Research has yet to be reported on using this method to invert the complex refractive index of nanoparticles. This paper reports the feasibility and reliability of the contour intersection method in the inversion of the complex refractive index of nanoparticles using Au-Ag alloy nanospheres. The Mie theory and the size-dependent dielectric function are used to calculate the light scattering and absorption efficiency of Au-Ag alloy nanospheres corresponding to the complex refractive index. The complex refractive index of the particles is obtained by inversion with the contour intersection method. The backscattering efficiency constraint method is used to determine the unique solution when multiple valid solutions from the contour intersection method appear. The effects of the Au component percentage, particle size, and measurement errors on the inversion results are quantitatively analyzed. Finally, the inversion accuracy is compared and analyzed with the traditional iterative method. The results show that as long as the light scattering efficiency, light absorption efficiency, and backscattering efficiency of Au nanospheres can be measured, the accurate complex refractive index can also be calculated by inversion using the contour intersection method. The accuracy of the inversion results can be ensured when the measurement error is less than 5%. The results of inversion using the contour intersection method are better than those of the iterative methods under the same conditions. This study provides a simple and reliable inversion method for measuring the complex refractive index of Au-Ag alloy nanospheres.

Programmable Nanostructures Based on Framework-DNA for Applications in Biosensing

DNA has been actively utilized as bricks to construct exquisite nanostructures due to their unparalleled programmability. Particularly, nanostructures based on framework DNA (F-DNA) with controllable size, tailorable functionality, and precise addressability hold excellent promise for molecular biology studies and versatile tools for biosensor applications. In this review, we provide an overview of the current development of F-DNA-enabled biosensors. Firstly, we summarize the design and working principle of F-DNA-based nanodevices. Then, recent advances in their use in different kinds of target sensing with effectiveness have been exhibited. Finally, we envision potential perspectives on the future opportunities and challenges of biosensing platforms.

Optical Biosensors and Their Applications for the Detection of Water Pollutants

The correct detection and quantification of pollutants in water is key to regulating their presence in the environment. Biosensors offer several advantages, such as minimal sample preparation, short measurement times, high specificity and sensibility and low detection limits. The purpose of this review is to explore the different types of optical biosensors, focusing on their biological elements and their principle of operation, as well as recent applications in the detection of pollutants in water. According to our literature review, 33% of the publications used fluorescence-based biosensors, followed by surface plasmon resonance (SPR) with 28%. So far, SPR biosensors have achieved the best results in terms of detection limits. Although less common (22%), interferometers and resonators (4%) are also highly promising due to the low detection limits that can be reached using these techniques. In terms of biological recognition elements, 43% of the published works focused on antibodies due to their high affinity and stability, although they could be replaced with molecularly imprinted polymers. This review offers a unique compilation of the most recent work in the specific area of optical biosensing for water monitoring, focusing on both the biological element and the transducer used, as well as the type of target contaminant. Recent technological advances are discussed.

Microfluidic preparation of optical sensors for biomedical applications

Optical biosensors are platforms that translate biological information into detectable optical signals, and have extensive applications in various fields due to their characteristics of high sensitivity, high specificity, dynamic sensing, etc. The development of optical sensing materials is an important part of optical sensors. In this review, we emphasize the role of microfluidic technology in the preparation of optical sensing materials and the application of the derived optical sensors in the biomedical field. We first present some common optical sensing mechanisms and the functional responsive materials involved. Then, we describe the preparation of these sensing materials by microfluidics. Afterward, we enumerate the biomedical applications of these optical materials as biosensors in disease diagnosis, drug evaluation, and organ-on-a-chip. Finally, we discuss the challenges and prospects in this field.

Diagnosis of acute myocardial infarction: highlighting cardiac troponins as vital biomarkers

The molecular marker, cardiac troponin (cTn) is a complex protein that is attached to tropomyosin on the actin filament. It is an essential biomolecule in terms of the calcium-mediated regulation of the contractile apparatus in myofibrils, the release of which is an indication of the dysfunction of cardiomyocytes and hence the initiation of ischemic phenomena in the heart tissue. Fast and accurate analysis of cTn may help the diagnosis and management of acute myocardial infarction (AMI), for which electrochemical biosensors and microfluidics devices can be of great benefit. This editorial aims to highlight the importance of cTn as vital biomarkers in AMI diagnosis.

Improvement of Seed-Mediated Growth of Gold Nanoparticle Labels for DNA Membrane-Based Assays

Gold nanoparticles (AuNPs) are popular labels for colorimetric detection of various analytes, involving proteins, nucleic acids, viruses, and whole cells because of their outstanding optical properties, inertness, and modification variability. In this work, we present an improved approach for enhancement of color intensity for DNA membrane microarrays based on seed-mediated growth of AuNP labels. Biotin-labeled DNA is hybridized with capture oligonucleotide probes immobilized on the microarrays. Then biotin is revealed by a streptavidin-AuNP conjugate followed by the detection of AuNPs. Optimization of seed-mediated enlargement of AuNPs by the reduction of tetrachloroauric acid with hydroxylamine made it possible to change the coloring of specific spots on the microarrays from pink to a more contrasting black with minor background staining. Mean size of the resulting AuNPs was four times larger than before the enhancement. Adjusting the pH of HAuCl₄ solution to 3.5 and use of a large excess of hydroxylamine increased the signal/background ratio by several times. The method's applicability was demonstrated for quantification of a short oligonucleotide of 19 bases and full-length TEM-type β-lactamase genes of 860 bp responsible for the development of bacterial resistance against β-lactam antibiotics. Improved protocol for AuNP enlargement may be further transferred to any other membrane-based assays of nucleic acids with both instrumental and visual colorimetric detection.

Selenium-based nanomaterials for biosensing applications

The unique chemical and physical features of nanomaterials make them ideal for developing new and better sensing devices, particularly biosensors. Various types of nanoparticles, including metal, oxide, and semiconductor nanostructures, have been utilized to manufacture biosensors, and each kind of nanoparticle plays a unique role in the sensing system. Nanoparticles provide critical roles such as immobilizing biomolecules, catalyzing electrochemical processes, enhancing electron transport between electrode surfaces and proteins, identifying biomolecules, and even functioning as the reactant for the catalytic reaction. Among all the potential nanosystems to be used in biosensors, selenium nanoparticle (SeNP) features have sparked a growing interest in their use in bridging biological recognition events and signal transduction, as well as in developing biosensing devices with novel applications for identification, quantification, and study of different analytes of biological relevance. The optical, physical, and chemical characteristics of differently shaped SeNPs opened up a world of possibilities for developing biosensors of biomedical interest. The outstanding biocompatibility, conductivity, catalytic characteristics, high surface-to-volume ratio, and high density of SeNPs have enabled their widespread use in developing electrochemical biosensors with superior analytical performance compared to other designs of biosensors. This review summarizes recent and ongoing advances, current challenges, and future research perspectives on real-world applications of Se-based nanobiosensors to detect biologically relevant analytes such as hydrogen peroxide, heavy metals, or glucose. Due to the superior properties and multifunctionality of Se-NPs biosensors, these structures can open up considerable new horizons in the future of healthcare and medicine.

Nanozyme-based cascade SPR signal amplification for immunosensing of nitrated alpha-synuclein

A self-assembled nanozyme of iron porphyrin mediated supramolecular modified gold nanoparticles (FpA) was fabricated to determine nitrated alpha-synuclein as the Tyr 39 residue (nT39 α-Syn) of a potential biomarker for early diagnosis of Parkinson's disease (PD). Mechanically, localized surface plasmon resonance (LSPR) and the mass effect caused by catalytic deposition of the nanozyme contributed to a cascade signal amplification strategy. The sensor allowed a signal amplification and selective nT39 α-Syn bioanalysis with a 1.34-fold enhancement by cascade amplified SPR signal and double specific recognition. The detection limit was 1.78 ng/mL in the detection range of 7-240 ng/mL. Benefiting from the excellent immunosensor, this method can distinguish healthy people and PD patients using actual samples. Overall, this strategy provides a nanozyme-based biosensing platform for the early diagnosis of PD and can be applied to detect other protein biomarkers, such as PD-L1.

Label-free electrochemical microfluidic biosensors: futuristic point-of-care analytical devices for monitoring diseases

The integration of microfluidics with electrochemical analysis has resulted in the development of single miniaturized detection systems, which allows the precise control of sample volume with multianalyte detection capability in a cost- and time-effective manner. Microfluidic electrochemical sensing devices (MESDs) can potentially serve as precise sensing and monitoring systems for the detection of molecular markers in various detrimental diseases. MESDs offer several advantages, including (i) automated sample preparation and detection, (ii) low sample and reagent requirement, (iii) detection of multianalyte in a single run, (iv) multiplex analysis in a single integrated device, and (v) portability with simplicity in application and disposability. Label-free MESDs can serve an affordable real-time detection with a simple analysis in a short processing time, providing point-of-care diagnosis/detection possibilities in precision medicine, and environmental analysis. In the current review, we elaborate on label-free microfluidic biosensors, provide comprehensive insights into electrochemical detection techniques, and discuss the principles of label-free microfluidic-based sensing approaches.

Surface Plasmon Resonance Immunosensor with Antibody-Functionalized Magnetoplasmonic Nanoparticles for Ultrasensitive Quantification of the CD5 Biomarker

A surface plasmon resonance (SPR) immunosensor signal amplification strategy based on antibody-functionalized gold-coated magnetic nanoparticles (mAuNPs) was developed for ultrasensitive and quantitative detection of the CD5 biomarker using an indirect sandwich immunoassay format. The gold surface of the SPR sensor disk and mAuNPs was modified with a self-assembled monolayer of 11-mercaptoundecanoic acid (11-MUA), and the coupling method using N-(3-(dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide was used to immobilize capture antibodies against human CD5 (anti-CD5_2A) and detection antibodies against human CD5 (anti-CD5_2B), respectively. The mAuNPs and anti-CD5_2B conjugates (mAuNPs-anti-CD5_2B) were separated by an external magnetic field and used to amplify the SPR signal after the formation of the anti-CD5_2A/CD5 immune complex on the SPR sensor disk. Compared to the direct CD5 detection with a limit of detection (LOD) of 1.04 nM and a limit of quantification (LOQ) of 3.47 nM, the proposed sandwich immunoassay utilizing mAuNPs-anti-CD5_2B significantly improved the LOD up to 8.31 fM and the LOQ up to 27.70 fM. In addition, it showed satisfactory performance in human blood serum (recovery of 1.04 pM CD5 was 109.62%). These results suggest that the proposed signal amplification strategy has superior properties and offers the potential to significantly increase the sensitivity of the analysis.

Sensitive Oligonucleotide Detection Using Resonant Coupling between Fano Resonance and Image Dipoles of Gold Nanoparticles

The surface plasmon resonance (SPR)-based sensor has been widely used for biodetection. One of the attractive roles is the gold nanostructure with Fano resonance. Its sharp resonant profile takes advantage of the high figure of merit (FoM) in high-sensitivity detection. However, it is still difficult to detect small molecules at low concentrations due to the extremely low refractive index changes on the metallic surface. We propose using the coupling of image dipoles of gold nanoparticles (AuNPs) and Fano resonance of periodic capped gold nanoslits (CGNs) for sensitive small-molecule detections. The coupling mechanism was verified by three-dimensional finite-difference time-domain calculations and experiments. AuNPs on CGN form image dimer assemblies and induce image dipole with resonance wavelengths ranging from 730 to 550 nm. The surface plasmon polaritons (SPPs) interact with the image dipole of the AuNP on the CGNs and then scatter out through the periodic gold caps. The experimental results show that the peak intensity of grating resonance is decreased by the effect of image dipole and exhibits the maximum intensity change when the Fano resonance matches the resonance of image dipole. The 50 nm AuNPs can be detected with a surface density of less than one particle/μm² by using the intensity change as the signal. With the resonant coupling between Fano resonance and image dipole extinction, the oligonucleotide with a molecular weight of 5.5 kDa can be detected at a concentration of 100 fM. The resonant coupling dramatically pushes the sensitivity boundary, and we report the limit of detection (LOD) to be 3 orders of magnitude lower than that of the prism-based SPR. This study provides a promising and efficient method for detecting low concentrations of small molecules such as aptamers, miRNA, mRNA, and peptides.

Research Progress of Plasmonic Nanostructure-Enhanced Photovoltaic Solar Cells

Enhancement of the electromagnetic properties of metallic nanostructures constitute an extensive research field related to plasmonics. The latter term is derived from plasmons, which are quanta corresponding to longitudinal waves that are propagating in matter by the collective motion of electrons. Plasmonics are increasingly finding wide application in sensing, microscopy, optical communications, biophotonics, and light trapping enhancement for solar energy conversion. Although the plasmonics field has relatively a short history of development, it has led to substantial advancement in enhancing the absorption of the solar spectrum and charge carrier separation efficiency. Recently, huge developments have been made in understanding the basic parameters and mechanisms governing the application of plasmonics, including the effects of nanoparticles' size, arrangement, and geometry and how all these factors impact the dielectric field in the surrounding medium of the plasmons. This review article emphasizes recent developments, fundamentals, and fabrication techniques for plasmonic nanostructures while investigating their thermal effects and detailing light-trapping enhancement mechanisms. The mismatch effect of the front and back light grating for optimum light trapping is also discussed. Different arrangements of plasmonic nanostructures in photovoltaics for efficiency enhancement, plasmonics' limitations, and modeling performance are also deeply explored.

Influence of Random Plasmonic Metasurfaces on Fluorescence Enhancement

One of the strategies employed to increase the sensitivity of the fluorescence-based biosensors is to deposit chromophores on plasmonic metasurfaces which are periodic arrays of resonating nano-antennas that allow the control of the electromagnetic field leading to fluorescence enhancement. While artificially engineered metasurfaces realized by micro/nano-fabrication techniques lead to a precise tailoring of the excitation field and resonant cavity properties, the technological overhead, small areas, and high manufacturing cost renders them unsuitable for mass production. A method to circumvent these challenges is to use random distribution of metallic nanoparticles sustaining plasmonic resonances, which present the properties required to significantly enhance the fluorescence. We investigate metasurfaces composed of random aggregates of metal nanoparticles deposited on a silicon and glass substrates. The finite difference time domain simulations of the interaction of the incident electromagnetic wave with the structures reveals a significant enhancement of the excitation field, which is due to the resonant plasmonic modes sustained by the nanoparticles aggregates. We experimentally investigated the role of these structures in the fluorescent behaviour of Rhodamine 6G dispersed in polymethylmethacrylate finding an enhancement that is 423-fold. This suggests that nanoparticle aggregates have the potential to constitute a suitable platform for low-cost, mass-produced fluorescent biosensors.

Applications of hybridization chain reaction optical detection incorporating nanomaterials: A review

The development of powerful, simple and cost-effective signal amplifiers has significant implications for biological research and analysis. Hybridization chain reaction (HCR) has attracted increasing attention because of its enzyme-free, simple, and efficient amplification. In the HCR process, an initiator probe triggered a pair of metastable hairpins through a cross-opening process to propagate a chain reaction of hybridization events, yielding a long-nicked double-stranded nucleic acid structure. To achieve more noticeable signal amplification, nanomaterials, including graphene oxide, quantum dots, gold, silver, magnetic, and other nanoparticles, were integrated with HCR. Various types of colorimetric, fluorescence, plasmonic analyses or chemiluminescence optical sensing strategies incorporating nanomaterials have been developed to analyze various targets, such as nucleic acids, small biomolecules, proteins, and metal ions. This review summarized the recent advances of HCR technology pairing diverse nanomaterials in optical detection and discussed their challenges.

Heterogeneous sensing of post-translational modification enzymes by integrating the advantage of homogeneous analysis

Heterogeneous analysis has great application prospects in the detection of post-translational modification (PTM) enzymes with the advantages of signal enhancement, less sample demand, and high sensitivity and selectivity. Nevertheless, once the substrate was fixed on a solid interface, the steric hindrance might limit the approaching of catalytic center to the substrate, thus reducing the efficiency of PTM. Herein, we suggested that the avidin-modified interface could be used to develop heterogeneous sensing platforms with biotin-labeled substrates as the probes, in which the enzymatic PTM was performed in solution and the heterogeneous assay was conducted on a solid surface. The sensing strategy integrates the advantages but overcomes the defects of both homogeneous and heterogeneous assays. Protein kinase A (PKA) and histone acetyltransferase (HAT) were determined as the examples by using sequence-specific peptide substrates. The signal changes were monitored by HRP-based colorimetric assay and antibody-amplified surface plasmon resonance (SPR). The methods were used for analysis of cell lysates and evaluation of inhibition efficiency with satisfactory results. The strategy can be used for the detection of a variety of biological enzymes and provide a new idea for the design of various heterogeneous biosensors. Thus, this work should be of great significance to the popularization and practical application of biosensors.

Advances in Nanomaterial-based Biosensors for Determination of Glycated Hemoglobin

Diabetes is a major public health burden whose prevalence has been steadily increasing over the past decades. Glycated hemoglobin (HbA1c) is currently the gold standard for diagnostics and monitoring of glycemic control in diabetes patients. HbA1c biosensors are often considered to be cost-effective alternatives for smaller testing laboratories or clinics unable to access other reference methods. Many of these sensors deploy nanomaterials as recognition elements, detection labels, and/or transducers for achieving sensitive and selective detection of HbA1c. Nanomaterials have emerged as important sensor components due to their excellent optical and electrical properties, tunable morphologies, and easy integration into multiple sensing platforms. In this review, we discuss the advantages of using nanomaterials to construct HbA1c sensors and various sensing strategies for HbA1c measurements. Key gaps between the current technologies with what is needed moving forward are also summarized.

Application of Lab-on-Chip for Detection of Microbial Nucleic Acid in Food and Environment

Various diseases caused by food-borne or environmental pathogenic microorganisms have been a persistent threat to public health and global economies. It is necessary to regularly detect microorganisms in food and environment to prevent infection of pathogenic microorganisms. However, most traditional detection methods are expensive, time-consuming, and unfeasible in practice in the absence of sophisticated instruments and trained operators. Point-of-care testing (POCT) can be used to detect microorganisms rapidly on site and greatly improve the efficiency of microbial detection. Lab-on-chip (LOC) is an emerging POCT technology with great potential by integrating most of the experimental steps carried out in the laboratory into a single monolithic device. This review will primarily focus on principles and techniques of LOC for detection of microbial nucleic acid in food and environment, including sample preparation, nucleic acid amplification and sample detection.

Settling dynamics of nanoparticles in simple and biological media

The biological response of organisms exposed to nanoparticles is often studied in vitro using adherent monolayers of cultured cells. In order to derive accurate concentration-response relationships, it is important to determine the local concentration of nanoparticles to which the cells are actually exposed rather than the nominal concentration of nanoparticles in the cell culture medium. In this study, the sedimentation-diffusion process of different sized and charged gold nanoparticles has been investigated in vitro by evaluating their settling dynamics and by developing a theoretical model to predict the concentration depth profile of nanoparticles in solution over time. Experiments were carried out in water and in cell culture media at a range of controlled temperatures. The optical phenomenon of caustics was exploited to track nanoparticles in real time in a conventional optical microscope without any requirement for fluorescent labelling that potentially affects the dynamics of the nanoparticles. The results obtained demonstrate that size, temperature and the stability of the nanoparticles play a pivotal role in regulating the settling dynamics of nanoparticles. For gold nanoparticles larger than 60 nm in diameter, the initial nominal concentration did not accurately represent the concentration of nanoparticles local to the cells. Finally, the theoretical model proposed accurately described the settling dynamics of the nanoparticles and thus represents a promising tool to support the design of in vitro experiments and the study of concentration-response relationships.

Enhanced Plasmonic Biosensor Utilizing Paired Antibody and Label-Free Fe3O4 Nanoparticles for Highly Sensitive and Selective Detection of Parkinson's α-Synuclein in Serum

Parkinson’s disease (PD) is an acute and progressive neurodegenerative disorder, and diagnosis of the disease at its earliest stage is of paramount importance to improve the life expectancy of patients. α-Synuclein (α-syn) is a potential biomarker for the early diagnosis of PD, and there is a great need to develop a biosensing platform that precisely detects α-syn in human body fluids. Herein, we developed a surface plasmon resonance (SPR) biosensor based on the label-free iron oxide nanoparticles (Fe₃O₄ NPs) and paired antibody for the highly sensitive and selective detection of α-syn in serum samples. The sensitivity of the SPR platform is enhanced significantly by directly depositing Fe₃O₄ NPs on the Au surface at a high density to increase the decay length of the evanescent field on the Au film. Moreover, the utilization of rabbit-type monoclonal antibody (α-syn-RmAb) immobilized on Au films allows the SPR platform to have a high affinity-selectivity binding performance compared to mouse-type monoclonal antibodies as a common bioreceptor for capturing α-syn molecules. As a result, the current platform has a detection limit of 5.6 fg/mL, which is 20,000-fold lower than that of commercial ELISA. The improved sensor chip can also be easily regenerated to repeat the α-syn measurement with the same sensitivity. Furthermore, the SPR sensor was applied to the direct analysis of α-syn in serum samples. By using a format of paired α-syn-RmAb, the SPR sensor provides a recovery rate in the range from 94.5% to 104.3% to detect the α-syn in diluted serum samples precisely. This work demonstrates a highly sensitive and selective quantification approach to detect α-syn in human biofluids and paves the way for the future development in the early diagnosis of PD.

SPR detection of protein enhanced by seedless synthesized gold nanorods

Surface plasmon resonance (SPR) is a label-free, real-time bio-sensing technique with high potential in the diagnostic area, especially when a signal amplification strategy is used to improve the detection limit. We report here a simple method for enhancing the detection limit of bovine serum albumin (BSA), by attaching gold nanorods (AuNRs). AuNRs were obtained by a seedless synthesis technique and characterized using scanning electron microscopy (SEM), UV-VIS spectroscopy, FT-IR spectroscopy and dynamic light scattering (DLS). Finite element method (FEM) simulations were employed to explore the enhancement of the SPR signal by adding AuNRs on the SPR sensor's metallic layer. SPR spectroscopy was used to analyze the changes in the refractive index brought by the immobilization of unconjugated BSA and BSA modified with AuNRs. The results confirmed that the AuNRs conjugated with the protein increase the SPR signal ~ 10 times, leading to a limit of detection of 1.081 × 10^-8 M (0.713 μg/mL).

A novel colorimetric biosensor for sensitive detection of aflatoxin mediated by bacterial enzymatic reaction in saffron samples

Aflatoxin is regarded as the potent carcinogenic agent which is secreted from fungi and present in some food products. So far, many detection methods have been developed to determine the trace amounts of aflatoxin in foods. In the present study a colorimetric competitive assay for detection of aflatoxin B1 (AFB1) has been developed based on interaction of gelatin functionalized gold nanoparticles (AuNPs@gelatin) in specific enzymatic reaction. Bacterial supernatant containing gelatinase enzyme were used as the substrate that could digest the coated gelatin on the surface of AuNPs and following in the presence of NaCl medium ingredient resulted to color change of AuNPs colloidal solution from red to purple. It was observed that with addition of aflatoxin to the bacterial supernatant, aflatoxin could interfere in aggregation of AuNPs and inhibited the process which subsequently prevent the expected color change induced by AuNPs aggregation. The supernatant containing AuNPs were investigated to analyze their induced surface plasmon resonance spectra through UV-visible spectroscopy. The absorption values were directly proportional with the applied AFB1 concentration. The experiment conditions including incubation time, AuNPs concentration and pH were investigated. The obtained results showed that through this approach we could detect the AFB1 in a linear range from 10 to 140 pg ml^-1, with detection limit of 4 pg ml^-1. Real sample assay in saffron samples showed recoveries percentage of 92.4%-95.3%. The applied approach proposed simple, cost effective and specific method for detection of AFB1 toxin in food samples.

Progress and prospects of magnetic iron oxide nanoparticles in biomedical applications: A review

Nanoscience has been considered as one of the most substantial research in modern science. The utilization of nanoparticle (NP) materials provides numerous advantages in biomedical applications due to their unique properties. Among various types of nanoparticles, the magnetic nanoparticles (MNPs) of iron oxide possess intrinsic features, which have been efficiently exploited for biomedical purposes including drug delivery, magnetic resonance imaging, Magnetic-activated cell sorting, nanobiosensors, hyperthermia, and tissue engineering and regenerative medicine. The size and shape of nanostructures are the main factors affecting the physicochemical features of superparamagnetic iron oxide nanoparticles, which play an important role in the improvement of MNP properties, and can be controlled by appropriate synthesis strategies. On the other hand, the proper modification and functionalization of the surface of iron oxide nanoparticles have significant effects on the improvement of physicochemical and mechanical features, biocompatibility, stability, and surface activity of MNPs. This review focuses on popular methods of fabrication, beneficial surface coatings with regard to the main required features for their biomedical use, as well as new applications.

Detection of Tumor DNA in Human Plasma with a Functional PLL-Based Surface Layer and Plasmonic Biosensing

Standard protocols for the analysis of circulating tumor DNA (ctDNA) include the isolation of DNA from the patient's plasma and its amplification and analysis in buffered solutions. The application of such protocols is hampered by several factors, including the complexity and time-constrained preanalytical procedures, risks for sample contamination, extended analysis time, and assay costs. A recently introduced nanoparticle-enhanced surface plasmon resonance imaging-based assay has been shown to simplify procedures for the direct detection of tumor DNA in the patient's plasma, greatly simplifying the cumbersome preanalytical phase. To further simplify the protocol, a new dual-functional low-fouling poly-l-lysine (PLL)-based surface layer has been introduced that is described herein. The new PLL-based layer includes a densely immobilized CEEEEE oligopeptide to create a charge-balanced system preventing the nonspecific adsorption of plasma components on the sensor surface. The layer also comprises sparsely attached peptide nucleic acid probes complementary to the sequence of circulating DNA, e.g., the analyte that has to be captured in the plasma from cancer patients. We thoroughly investigated the contribution of each component of the dual-functional polymer to the antifouling properties of the surface layer. The low-fouling property of the new surface layer allowed us to detect wild-type and KRAS p.G12D-mutated DNA in human plasma at the attomolar level (∼2.5 aM) and KRAS p.G13D-mutated tumor DNA in liquid biopsy from a cancer patient with almost no preanalytical treatment of the patient's plasma, no need to isolate DNA from plasma, and without PCR amplification of the target sequence.

High-Order Multimode Waveguide Interferometer for Optical Biosensing Applications

A generalization of the concept of multimode interference sensors is presented here for the first time, to the best of our knowledge. The existing bimodal and trimodal sensors correspond to particular cases of those interference sensors. A thorough study of the properties of the multimode waveguide section provided a deeper insight into the behavior of this class of sensors, which allowed us to establish new criteria for designing more sensitive structures. Other challenges of using high-order modes within the sensing area of the device reside in the excitation of these modes and the interpretation of the output signal. To overcome these, we developed a novel structure to excite any desired high-order mode along with the fundamental mode within the sensing section, while maintaining a fine control over the power distribution between them. A new strategy to detect and interpret the output signal is also presented in detail. Finally, we designed a high-order sensor for which numerical simulations showed a theoretical limit of detection of 1.9×10−7 RIU, making this device the most sensitive multimode interference sensor reported so far.

The Microbiome Meets Nanotechnology: Opportunities and Challenges in Developing New Diagnostic Devices

Monitoring of the human microbiome is an emerging area of diagnostics for personalized medicine. Here, the potential of different nanomaterials and nanobiosensing technologies is reviewed for the development of novel diagnostic devices for the detection and measurement of microbiome-related biomarkers. Moreover, the current and future landscape of microbiome-based diagnostics is defined by exploring the advantages and disadvantages of current nanotechnology-based approaches, especially in the context of developing point-of-care (PoC) devices that would meet the international guidelines known as REASSURED (Real-time connectivity; Ease of specimen collection; Affordability; Sensitivity; Specificity; User-friendliness; Rapid & robust operation; Equipment-free; and Deliverability). Finally, the strategies of the latest international scientific consortia working in this field are analyzed, the current microbiome diagnostics market are reported and the principal ethical, legal, and societal issues related to microbiome R&D and innovation are discussed.

Nanodiagnostic Attainments and Clinical Perspectives on C-Reactive Protein: Cardiovascular Disease Risks Assessment

Cardiovascular disease (CVD) has become one of the leading causes of morbidity and mortality in both men and women. According to the World Health Organization (WHO), ischemic heart disease is the major issue due to the narrowing of the coronary artery by plaque formation on the artery wall, which causes an inadequate flow of oxygen and blood to the heart and is called 'coronary artery disease'. The CVD death rate increased by up to 15% in 2016 (~17.6 million) compared to the past decade. This tremendous increment urges the development of a suitable biomarker for rapid and early diagnosis. Currently, C-reactive protein (CRP) is considered an outstanding biomarker for quick and accurate outcomes in clinical analyses. Various techniques have also been used to diagnose CVD, including surface plasmon resonance (SPR), colorimetric assay, enzyme-linked immunosorbent assay (ELISA), fluoro-immunoassays, chemiluminescent assays, and electrical measurements. This review discusses such diagnostic strategies and how current, cutting-edge technologies have enabled the development of high-performance detection methodologies. Concluding remarks have been made concerning the clinical significance and the use of nanomaterial in medical diagnostics towards nanotheranostics.

Rapid, simultaneous detection of mycotoxins with smartphone recognition-based immune microspheres

How to achieve simultaneous and rapid detection of various mycotoxins in food has important practical significance in the field of food processing and safety. In this paper, a smartphone immunoassay system based on hydrogel microspheres has been constructed to quickly detect two mycotoxins at the same time. The rapid detection system was reflected in the following three processes: (1) rapid separation of free matter after direct competition reaction based on hydrogel solid-phase carrier particles; (2) rapid detection process based on efficient catalytic function of enzymes; (3) fast capture and analysis of images based on smartphone software. Ochratoxin A (OTA) and zearalenone (ZEN) are secondary toxic metabolites of fungi that can contaminate a wide range of foods and feeds. OTA and ZEN were used as detection model molecules to verify the feasibility of the intelligent rapid detection system. The entire detection process was within 30 min, and the results were analyzed in only 10 s. Detection limits of mycotoxins OTA and ZEN are 0.7711 ng L^-1 and 1.0391 ng L^-1. The recoveries of both mycotoxins ranged from 76.72 to 122.05%. This study provides a universal rapid detection method for on-site application of large-scale food security testing. Schematic diagram of the construction of the smartphone detection system: The system is divided into three parts: detection, image capture and analysis, and result.

Biosensing Amplification by Hybridization Chain Reaction on Phase-Sensitive Surface Plasmon Resonance

Surface Plasmon Resonance (SPR) is widely used in biological and chemical sensing with fascinating properties. However, the application of SPR to detect trace targets is hampered by non-specific binding and poor signal. A variety of approaches for amplification have been explored to overcome this deficiency including DNA aptamers as versatile target detection tools. Hybridization chain reaction (HCR) is a high-efficiency enzyme-free DNA amplification method operated at room temperature, in which two stable species of DNA hairpins coexist in solution until the introduction of the initiator strand triggers a cascade of hybridization events. At an optimal salt condition, as the concentrations of H1 and H2 increased, the HCR signals were enhanced, leading to signal amplification reaching up to 6.5-fold of the detection measure at 30 min. This feature enables DNA to act as an amplifying transducer for biosensing applications to provide an enzyme-free alternative that can easily detect complex DNA sequences. Improvement of more diverse recognition events can be achieved by integrating HCR with a phase-sensitive SPR (pSPR)-tested aptamer stimulus. This work seeks to establish pSPR aptamer system for highly informative sensing by means of an amplification HCR. Thus, combining pSPR and HCR technologies provide an expandable platform for sensitive biosensing.