Gold Nanoparticles Based Optical Biosensors for Cancer Biomarker Proteins: A Review of the Current Practices

The integration platform for exosome capture and colorimetric detection: Site occupying effect-modulated MOF-aptamer interaction and aptamer-Au NPs-dopamine interaction

Exosomes are extracellular vesicles of 30-200 nm in diameter that inherit molecular markers from their parent cells, including proteins, lipids, nucleic acids, and glycoconjugates. The detection and protein profiling of exosome could provide noninvasive access to disease diagnosis and treatment. In recent years, it has been found that Zr-MOFs can capture exosomes by forming Zr-O-P bonds through the phospholipid bilayer of exosomes. In addition, gold nanoparticles with optical response are used for colorimetric biological analysis, such as proteins, peptides, DNA. In this work, we proposed an aptasensor for exosome capture and sensitive colorimetric detection. The Zr-MOF (PCN-224) is innovatively used to capture exosome by Zr-O-P bond, and sodium tripolyphosphate (STPP) is used to block the non-specific adsorption of DNA aptamers on the surface of PCN-224 by site occupying effect. The aptamer binds to exosome immunity, and the remaining aptamer binds to Au NPs, resulting in an increase in steric hindrance and electrostatic repulsion, which makes the dispersion of Au NPs better and avoids the aggregation of Au NPs induced by dopamine (DA). The ratio of absorbance A650/A520 represents the aggregate degree of Au NPs, which correlates with the concentration of exosomes, and achieves sensitive colorimetric detection of exosomes with a linear range of 1.0 × 105-1.0 × 107 particles/mL. Further studies reveal that our work has excellent selectivity and anti-interference, breast cancer patients and healthy individuals can be distinguished by analyzing the differences in the expression of CD63 protein on exosome. The proposed biosensor integrates the capture and detection of exosomes, the multiple colors of Au NPs changed significantly from red to gray, which was conducive to the naked-eye identification of exosome detection.

One-step, rapid, nanoparticle-based biosensor platform for the simultaneous identification of hepatitis B virus and hepatitis C virus in clinical applications

OBJECTIVES

Viral hepatitis caused by hepatitis B virus (HBV) and hepatitis C virus (HCV) infections remain a major global public health challenge, particularly in low- and middle-income countries. It is crucial to utilize a pointof-care (POC) testing platform that is sensitive, specific, rapid, and user-friendly for screening and diagnosis of the two infections. Here, a novel molecular diagnostic assay, integrating multiplex loop-mediated isothermal amplification with a gold nanoparticle-based lateral flow biosensor (mLAMP-AuNPs-LFB) was developed and applied for one-step, visual, rapid, sensitive, and specific identification of HBV and HCV.

METHODS

The AuNPs-based LFB was devised and constructed for the simultaneous detection of HBV and HCV. The HBV-LAMP and HCV-LAMP primers were designed against the S and 5'-untranslated region (5'-UTR) genes from the major HBV genotypes (B, C, D, B/C recombinant, and C/D recombinant) and HCV subtypes (1b, 2a, 3a, 3b, and 6a) in China, respectively. Our assay conditions, both multiplex-LAMP amplification temperature and time were optimized. The sensitivity and specificity of our assay were tested, and the feasibility of our assay was verified through clinical samples.

RESULTS

The AuNPs-based LFB used here was successfully manufactured according to our devise manual. The two unique independent primer pairs were successfully designed based on the S and 5'-UTR genes, respectively. The optimal mLAMP-AuNPs-LFB detection process, involving rapid nucleic acid isolation (10 min), mLAMP (63 °C for 35 min), and visual AuNPs-LFB interpretation (less than 2 min), could be completed within 50 min. The HBV&HCV-mLAMP-AuNPs-LFB assay can detect the target genes (HBV-S and HCV-5'-UTR) with as low as 20 copies of plasmid template per test, and the specificity was 100% for the experimental pathogens.

CONCLUSIONS

The preliminary results manifested that our mLAMP-AuNPs-LFB assay is a valuable tool and has tremendous potential as a POC testing approach for HBV and HCV identification, especially in undeveloped regions.

Uncoated gold nanoparticles create fewer and less localized defects in model prokaryotic than in model eukaryotic lipid membranes

The rise of the populations of antibiotic resistant bacteria represents an increasing threat to human health. In addition to the synthesis of new antibiotics, which is an extremely expensive and time-consuming process, one of the ways to combat bacterial infections is the use of gold nanoparticles (Au NPs) as the vehicles for targeted delivery of therapeutic drugs. Since such a strategy requires the investigation of the effect of Au NPs (with and without drugs) on both bacterial and human cells, we investigated how the presence of coating-free Au NPs affects the physicochemical properties of lipid membranes that model prokaryotic (PRO) and eukaryotic (EU) cells. PRO/EU systems prepared as multilamellar liposomes (MLVs) and hybrid structures (HSs) from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylglycerol (DPPG)/1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS) in the absence (MLVs)/presence (HSs) of differently distributed Au NPs (sizes ∼20 nm) reported stabilization of the gel phase of PRO systems in comparison with EU one (DSC data of PRO/EU were Tm(MLVs) ≈ 41.8 °C/42.0 °C, Tm¯ (HSs) ≈ 43.1 °C/42.4 °C, whereas UV-Vis response Tm(MLVs) ≈ 41.5 °C/42.0 °C, Tm¯ (HSs) ≈ 42.9 °C/41.1 °C). Vibrational spectroscopic data unraveled a substantial impact of Au NPs on the non-polar part of lipid bilayers, emphasizing the increase of kink and gauche conformers of the hydrocarbon chain. By interpreting the latter as Au NPs-induced defects, which exert the greatest effect when Au NPs are found exclusively outside the lipid membrane, these findings suggested that Au NPs reduced the compactness of EU-based lipid bilayers much more than in analogous PRO systems. Since the uncoated Au NPs manifested adverse effects when applied as antimicrobials, the results obtained in this work contribute towards recognizing AuNP functionalization as a strategy in tuning and reversing this effect.

Biotechnological advances in microbial synthesis of gold nanoparticles: Optimizations and applications

This review discusses the eco-friendly and cost-effective biosynthesis of gold nanoparticles (AuNPs) in viable microorganisms, focusing on microbes-mediated AuNP biosynthesis. This process suits agricultural, environmental, and biomedical applications, offering renewable, eco-friendly, non-toxic, sustainable, and time-efficient methods. Microorganisms are increasingly used in green technology, nanotechnology, and RNAi technology, but several microorganisms have not been fully identified and characterized. Bio-nanotechnology offers eco-friendly and sustainable solutions for nanomedicine, with microbe-mediated nanoparticle biosynthesis producing AuNPs with anti-oxidation activity, stability, and biocompatibility. Ultrasmall AuNPs offer rapid distribution, renal clearance, and enhanced permeability in biomedical applications. The review explores nano-size dependent biosynthesis of AuNPs by bacteria, fungi, and viruses revealing their non-toxic, non-genotoxic, and non-oxidative properties on human cells. AuNPs with varying sizes and shapes, from nitrate reductase enzymes, have shown potential as a promising nano-catalyst. The synthesized AuNPs, with negative charge capping molecules, have demonstrated antibacterial activity against drug-resistant Pseudomonas aeruginosa, and Acinetobacter baumannii strains, and were non-toxic to Vero cell lines, indicating potential antibiotic resistance treatments. A green chemical method for the biosynthesis of AuNPs using reducing chloroauric acid and Rhizopus oryzae protein extract has been described, demonstrating excellent stability and strong catalytic activity. AuNPs are eco-friendly, non-toxic, and time-efficient, making them ideal for biomedical applications due to their antioxidant, antidiabetic, and antibacterial properties. In addition to the biomedical application, the review also highlights the role of microbially synthesized AuNPs in sustainable management of plant diseases, and environmental bioremediation.

Selective and naked eye colorimetric detection of creatinine through aptamer-based target-induced passivation of gold nanoparticles

We report a simple naked eye colorimetric detection assay developed for the small molecule creatinine using the surface passivation of gold nanoparticles (AuNPs) which is conjugated with a creatinine binding aptamer. The selective binding of creatinine to aptamer sequences causes a decrease in the catalytic activity of AuNPs, and the color change time of the 4-nitrophenol reduction was used for the quantitative colorimetric detection of creatinine. Herein, the surfaces of AuNPs acted as the catalyst for the reduction of 4-nitrophenol (yellow) to 4-aminophenol (colorless), and the passivation with creatinine bound aptamer sequences delayed the reduction. The developed assay was able to detect creatinine in a linear range of 2-20 mM with a limit of detection of 0.87 mM. The developed colorimetric assay was very selective and repeatable and could detect creatinine in the presence of interfering biomolecules. Moreover, the assay showed excellent results for the analysis of creatinine in artificial urine samples. The developed assay can be used as a point of care (POC) device for the naked eye detection of creatinine within few minutes without any instrument support.

Carrier cascade target delivery of 5-aminolevulinic acid nanoplatform to enhance antitumor efficiency of photodynamic therapy against lung cancer

5-Aminolevulinic acid (5-ALA) is a prodrug of porphyrin IX (PpIX). Disadvantages of 5-ALA include poor stability, rapid elimination, poor bioavailability, and weak cell penetration, which greatly reduce the clinical effect of 5-ALA based photodynamic therapy (PDT). Presently, a novel targeting nanosystem was constructed using gold nanoparticles (AuNPs) as carriers loaded with a CSNIDARAC (CC9)-targeting peptide and 5-ALA via Au-sulphur and ionic bonds, respectively, and then wrapped in polylactic glycolic acid (PLGA) NPs via self-assembly to improve the antitumor effects and reduce the side effect. The successful preparation of ALA/CC9@ AuNPs-PLGA NPs was verified using ultraviolet-visible, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The analyses revealed good sphericity with a particle size of approximately140 nm, Zeta potential of 10.11 mV, and slow-controlled release characteristic in a weak acid environment. Confocal microscopy revealed targeting of NCL-H460 cells by NPs by actively internalising CC9 and avoiding the phagocytic action of RAW264.7 cells, and live fluorescence imaging revealed targeting of tumours in tumour-bearing mice. Compared to free 5-ALA, the nanosystem displayed amplified anticancer activity by increasing production of PpIX and reactive oxygen species to induce mitochondrial pathway apoptosis. Antitumor efficacy was consistently observed in three-dimensionally cultured cells as the loss of integrity of tumour balls. More potent anti-tumour efficacy was demonstrated in xenograft tumour models by decreased growth rate and increased tumour apoptosis. Histological analysis showed that this system was not toxic, with lowered liver toxicity of 5-ALA. Thus, ALA/CC9@AuNPs-PLGA NPs deliver 5-ALA via a carrier cascade, with excellent effects on tumour accumulation and PDT through passive enhanced permeability and retention action and active targeting. This innovative strategy for cancer therapy requires more clinical trials before being implemented.

Recent Advancements in Biosensors for the Detection and Characterization of Amyloids: A Review

Modern medicine has increased the human lifespan. However, with an increase in average lifespan risk of amyloidosis increases. Amyloidosis is a condition characterized by protein misfolding and aggregation. Early detection of amyloidosis is crucial, yet conventional diagnostic methods are costly and lack precision, necessitating innovative tools. This review explores recent advancements in diverse amyloid detection methodologies, highlighting the need for interdisciplinary research to develop a miniaturized electrochemical biosensor leveraging nanotechnology. However, the diagnostics industry faces obstacles such as skilled labor shortages, standardized selection processes, and concurrent multi-analyte identification challenges. Research efforts are focused on integrating electrochemical techniques into clinical applications and diagnostics, with the successful transition of miniaturized technologies from development to testing posing a significant hurdle. Label-free transduction techniques like voltammetry and electrochemical impedance spectroscopy (EIS) have gained traction due to their rapid, cost-effective, and user-friendly nature.

Emerging Applications of Nanoparticles in the Diagnosis and Treatment of Breast Cancer

Breast cancer remains the most prevalent cancer among women worldwide, driving the urgent need for innovative approaches to diagnosis and treatment. This review highlights the pivotal role of nanoparticles in revolutionizing breast cancer management through advancements of interconnected approaches including targeted therapy, imaging, and personalized medicine. Nanoparticles, with their unique physicochemical properties, have shown significant promise in addressing current treatment limitations such as drug resistance and nonspecific systemic distribution. Applications range from enhancing drug delivery systems for targeted and sustained release to developing innovative diagnostic tools for early and precise detection of metastases. Moreover, the integration of nanoparticles into photothermal therapy and their synergistic use with existing treatments, such as immunotherapy, illustrate their transformative potential in cancer care. However, the journey towards clinical adoption is fraught with challenges, including the chemical feasibility, biodistribution, efficacy, safety concerns, scalability, and regulatory hurdles. This review delves into the current state of nanoparticle research, their applications in breast cancer therapy and diagnosis, and the obstacles that must be overcome for clinical integration.

Increasing the sensitivity and accuracy of detecting exosomes as biomarkers for cancer monitoring using optical nanobiosensors

The advancement of nanoscience and material design in recent times has facilitated the creation of point-of-care devices for cancer diagnosis and biomolecule sensing. Exosomes (EXOs) facilitate the transfer of bioactive molecules between cancer cells and diverse cells in the local and distant microenvironments, thereby contributing to cancer progression and metastasis. Specifically, EXOs derived from cancer are likely to function as biomarkers for early cancer detection due to the genetic or signaling alterations they transport as payload within the cancer cells of origin. It has been verified that EXOs circulate steadily in bodily secretions and contain a variety of information that indicates the progression of the tumor. However, acquiring molecular information and interactions regarding EXOs has presented significant technical challenges due to their nanoscale nature and high heterogeneity. Colorimetry, surface plasmon resonance (SPR), fluorescence, and Raman scattering are examples of optical techniques utilized to quantify cancer exosomal biomarkers, including lipids, proteins, RNA, and DNA. Many optically active nanoparticles (NPs), predominantly carbon-based, inorganic, organic, and composite-based nanomaterials, have been employed in biosensing technology. The exceptional physical properties exhibited by nanomaterials, including carbon NPs, noble metal NPs, and magnetic NPs, have facilitated significant progress in the development of optical nanobiosensors intended for the detection of EXOs originating from tumors. Following a summary of the biogenesis, biological functions, and biomarker value of known EXOs, this article provides an update on the detection methodologies currently under investigation. In conclusion, we propose some potential enhancements to optical biosensors utilized in detecting EXO, utilizing various NP materials such as silicon NPs, graphene oxide (GO), metal NPs, and quantum dots (QDs).

Development of a biophotonic fiber sensor using direct-taper and anti-taper techniques with seven-core and four-core fiber for the detection of doxorubicin in cancer treatment

Doxorubicin (DOX) is an important drug for cancer treatment, but its clinical application is limited due to its toxicity and side effects. Therefore, detecting the concentration of DOX during treatment is crucial for enhancing efficacy and reducing side effects. In this study, the authors developed a biophotonic fiber sensor based on localized surface plasmon resonance (LSPR) with the multimode fiber (MMF)-four core fiber (FCF)-seven core fiber (SCF)-MMF-based direct-taper and anti-taper structures for the specific detection of DOX. Compared to other detection methods, it has the advantages of high sensitivity, low cost, and strong anti-interference ability. In this experiment, multi-walled carbon nanotubes (MWCNTs), cerium-oxide nanorods (CeO2-NRs), and gold nanoparticles (AuNPs) were immobilized on the probe surface to enhance the sensor's biocompatibility. MWCNTs and CeO2-NRs provided more binding sites for the fixation of AuNPs. By immobilizing AuNPs on the surface, the LSPR was stimulated by the evanescent field to detect DOX. The sensor surface was functionalized with DOX aptamers for specific detection, enhancing its specificity. The experiments demonstrated that within a linear detection range of 0-10 µM, the sensitivity of the sensor is 0.77 nm/µM, and the limit of detection (LoD) is 0.42 µM. Additionally, the probe's repeatability, reproducibility, stability, and selectivity were evaluated, indicating that the probe has high potential for detecting DOX during cancer treatment.

Detection of Sialic Acid to Differentiate Cervical Cancer Cell Lines Using a Sambucus nigra Lectin Biosensor

Pap smear screening is a widespread technique used to detect premalignant lesions of cervical cancer (CC); however, it lacks sensitivity, leading to identifying biomarkers that improve early diagnosis sensitivity. A characteristic of cancer is the aberrant sialylation that involves the abnormal expression of α2,6 sialic acid, a specific carbohydrate linked to glycoproteins and glycolipids on the cell surface, which has been reported in premalignant CC lesions. This work aimed to develop a method to differentiate CC cell lines and primary fibroblasts using a novel lectin-based biosensor to detect α2,6 sialic acid based on attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and chemometric. The biosensor was developed by conjugating gold nanoparticles (AuNPs) with 5 µg of Sambucus nigra (SNA) lectin as the biorecognition element. Sialic acid detection was associated with the signal amplification in the 1500-1350 cm-1 region observed by the surface-enhanced infrared absorption spectroscopy (SEIRA) effect from ATR-FTIR results. This region was further analyzed for the clustering of samples by applying principal component analysis (PCA) and confidence ellipses at a 95% interval. This work demonstrates the feasibility of employing SNA biosensors to discriminate between tumoral and non-tumoral cells, that have the potential for the early detection of premalignant lesions of CC.

Research Progress of Polysaccharide-Gold Nanocomplexes in Drug Delivery

Clinical drug administration aims to deliver drugs efficiently and safely to target tissues, organs, and cells, with the objective of enabling their therapeutic effects. Currently, the main approach to enhance a drug's effectiveness is ensuring its efficient delivery to the intended site. Due to the fact that there are still various drawbacks of traditional drug delivery methods, such as high toxicity and side effects, insufficient drug specificity, poor targeting, and poor pharmacokinetic performance, nanocarriers have emerged as a promising alternative. Nanocarriers possess significant advantages in drug delivery due to their size tunability and surface modifiability. Moreover, nano-drug delivery systems have demonstrated strong potential in terms of prolonging drug circulation time, improving bioavailability, increasing drug retention at the tumor site, decreasing drug resistance, as well as reducing the undesirable side effects of anticancer drugs. Numerous studies have focused on utilizing polysaccharides as nanodelivery carriers, developing delivery systems based on polysaccharides, or exploiting polysaccharides as tumor-targeting ligands to enhance the precision of nanoparticle delivery. These types of investigations have become commonplace in the academic literature. This review aims to elucidate the preparation methods and principles of polysaccharide gold nanocarriers. It also provides an overview of the factors that affect the loading of polysaccharide gold nanocarriers with different kinds of drugs. Additionally, it outlines the strategies employed by polysaccharide gold nanocarriers to improve the delivery efficiency of various drugs. The objective is to provide a reference for further development of research on polysaccharide gold nanodelivery systems.

Recent Advances in Metallic Nanostructures-assisted Biosensors for Medical Diagnosis and Therapy

The field of nanotechnology has witnessed remarkable progress in recent years, particularly in its application to medical diagnosis and therapy. Metallic nanostructures-assisted biosensors have emerged as a powerful and versatile platform, offering unprecedented opportunities for sensitive, specific, and minimally invasive diagnostic techniques, as well as innovative therapeutic interventions. These biosensors exploit the molecular interactions occurring between biomolecules, such as antibodies, enzymes, aptamers, or nucleic acids, and metallic surfaces to induce observable alterations in multiple physical attributes, encompassing electrical, optical, colorimetric, and electrochemical signals. These interactions yield measurable data concerning the existence and concentration of particular biomolecules. The inherent characteristics of metal nanostructures, such as conductivity, plasmon resonance, and catalytic activity, serve to amplify both sensitivity and specificity in these biosensors. This review provides an in-depth exploration of the latest advancements in metallic nanostructures-assisted biosensors, highlighting their transformative impact on medical science and envisioning their potential in shaping the future of personalized healthcare.

Antibody-labelled gold nanoparticles synthesized by laser ablation to detect SARS-CoV-2 antigen spike

Background and purpose

Rapid detection test via lateral flow immunoassay (LFIA) is employed as an alternate method to detect Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection. Gold nanoparticles (AuNPs), a vital component of LFIA, can be synthesized by laser ablation technique. This intense laser radiation may result in monodisperse gold nanoclusters, which are impurity-free and demonstrate innovative biocompatible surface chemistry. In this current research, laser-ablated AuNPs are produced and coupled with an anti-spike SARS-CoV-2 monoclonal antibody (mAb) generated in our prior study.

Experimental approach

The AuNPs from 30,000 shots of laser ablation exhibited a robust red color with a maximum absorbance peak at 520 nm. The performance of AuNPs-mAb conjugates as a signal reporter was then evaluated in half-stick LFIA.

Key results

The size distribution of AuNPs shows a relatively monodisperse and unimodal distribution with average particle diameters of 44.77 nm and a surface potential of -38.5 mV. The purified anti-spike mAb SARS-CoV-2 yielded two protein bands, representing the mAb heavy chain at 55 kDa and its light chain at 25 kDa. The immobilization of anti-spike mAb onto the surface of AuNPs revealed that 25 g/ml of mAb at phosphate buffer pH 9 was required to stabilize the AuNPs. The functional test of this conjugate was performed using dipstick LFIA, and the result shows that the AuNPs-mAb conjugates could successfully detect commercial spike antigen of SARS-CoV-2 at 10 ng level.

Conclusion

In this study, laser-ablated AuNPs were functionalized with anti-spike mAb SARS-CoV-2 and successfully used as a signal reporter in half-stick LFIA for detecting antigen spike SARS-CoV-2.

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.

Facile detection of botulinum neurotoxin using LSPR nanosensor based on Langmuir-Blodgett films of gold nanoparticles

In this exploratory study, Langmuir-Blodgett (LB) films of gold nanoparticles (Au NPs) were utilized for the first time to detect botulinum neurotoxin (BoNT) based on localized surface plasmon resonance (LSPR), acting as biosensors. Monolayers of Au NPs were initially transferred onto a transparent polymer substrate using the LB technique. This substrate was then used as the base material for subsequent depositions of capping ligands, and eventually, the BoNT at different concentrations. Upon each deposition, LSPR signals were recorded employing UV-Vis spectroscopy. As a result, it was demonstrated that the LB films transferred at a surface pressure of 35 mN m-1 were the optimal choice, capable of detecting BoNT at a concentration as low as 1 pg ml-1. Furthermore, it was discovered that the formation of Au NP clusters reduced the sensing capacity of the LB films. This sensor offers advantages such as easy fabrication and a quick detection process that utilizes visible light.

Green Ultrasound-Assisted Synthesis of Surface-Decorated Nanoparticles of Fe3O4 with Au and Ag: Study of the Antifungal and Antibacterial Activity

This work proposes a sonochemical biosynthesis of magnetoplasmonic nanostructures of Fe₃O₄ decorated with Au and Ag. The magnetoplasmonic systems, such as Fe₃O₄ and Fe₃O₄-Ag, were characterized structurally and magnetically. The structural characterizations reveal the magnetite structures as the primary phase. Noble metals, such as Au and Ag, are present in the sample, resulting in a structure-decorated type. The magnetic measurements indicate the superparamagnetic behavior of the Fe₃O₄-Ag and Fe₃O₄-Au nanostructures. The characterizations were carried out by X-ray diffraction and scanning electron microscopy. Complementarily, antibacterial and antifungal assays were carried out to evaluate the potential properties and future applications in biomedicine.

Solid-Phase Optical Sensing Techniques for Sensitive Virus Detection

Viral infections can pose a major threat to public health by causing serious illness, leading to pandemics, and burdening healthcare systems. The global spread of such infections causes disruptions to every aspect of life including business, education, and social life. Fast and accurate diagnosis of viral infections has significant implications for saving lives, preventing the spread of the diseases, and minimizing social and economic damages. Polymerase chain reaction (PCR)-based techniques are commonly used to detect viruses in the clinic. However, PCR has several drawbacks, as highlighted during the recent COVID-19 pandemic, such as long processing times and the requirement for sophisticated laboratory instruments. Therefore, there is an urgent need for fast and accurate techniques for virus detection. For this purpose, a variety of biosensor systems are being developed to provide rapid, sensitive, and high-throughput viral diagnostic platforms, enabling quick diagnosis and efficient control of the virus's spread. Optical devices, in particular, are of great interest due to their advantages such as high sensitivity and direct readout. The current review discusses solid-phase optical sensing techniques for virus detection, including fluorescence-based sensors, surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS), optical resonators, and interferometry-based platforms. Then, we focus on an interferometric biosensor developed by our group, the single-particle interferometric reflectance imaging sensor (SP-IRIS), which has the capability to visualize single nanoparticles, to demonstrate its application for digital virus detection.

Development of PEGylated Cu nanoclusters: A nontoxic, multifunctional colloidal system for bioimaging and peroxide sensing

This study introduces the development of blue-emitting colloidal Cu NCs through a novel and easy PEGylation method using different functional groups, including -SH and -COOH. The surface functionalization controls the size, cellular toxicity, and emission properties of Cu NCs. The combination of PEG, thiol, and carboxylic groups protects the particle surface from aggregation and oxidation. Among the samples, CAGP (Surface modified Cu NCs with -SH-COOH-PEG combination) emerges as an amazing candidate with the lowest toxicity and enhanced blue emission properties. The bright blue fluorescence emission from Hela cells after treatment with CAGP demonstrated this property. It also has excellent peroxide sensing potential, with a detection limit of 1.4 μM. Because of their excellent bioimaging and peroxide sensing properties, these Cu NCs could be a promising candidate for cellular oxidative stress sensing applications with high clinical relevance.

Humanoid shaped optical fiber plasmon biosensor functionalized with graphene oxide/multi-walled carbon nanotubes for histamine detection

Histamine is a biologically active molecule that serves as a reliable predictor of the quality of fish. In this work, authors have developed a novel humanoid-shaped tapered optical fiber (HTOF) biosensor based on the localized surface plasmon resonance (LSPR) phenomenon to detect varying histamine concentrations. In this experiment, a novel and distinctive tapering structure has been developed using a combiner manufacturing system and contemporary processing technologies. Graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) are immobilized on the HTOF probe surface to increase the biocompatibility of biosensor. In this instance, GO/MWCNTs are deployed first, then gold nanoparticles (AuNPs). Consequently, the GO/MWCNTs help to give abundant space for the immobilization of nanoparticles (AuNPs in this case) as well as increase surface area for the attachment of biomolecules to the fiber surface. By immobilizing AuNPs on the surface of the probe, the evanescent field can stimulate the AuNPs and excite the LSPR phenomena for sensing the histamine. The surface of the sensing probe is functionalized with diamine oxidase enzyme in order to enhance the histamine sensor's particular selectivity. The proposed sensor is demonstrated experimentally to have a sensitivity of 5.5 nm/mM and a detection limit of 59.45 µM in the linear detection range of 0-1000 µM. In addition, the probe's reusability, reproducibility, stability, and selectivity are tested; the results of these indices show that the probe has a high application potential for detecting histamine levels in marine products.

Simple immunosensor for ultrasensitive electrochemical determination of biomarker of the bone metabolism in human serum

Ultrasensitive and selective determination of biomarkers of the bone metabolism in serum is crucial for early screening, timely treatment, and monitoring of the curative effect of osteoporosis, which is a silent disease with serious health threats. Immunoassay with a simple sensing interface and ultrahigh sensitivity is highly desirable. Herein, a simple electrochemical immunosensor is demonstrated based on gold nanoparticles (AuNPs) electrodeposited on chitosan-reduced graphene oxide (CS-G) composite modified electrode, which can achieve sensitive determination of the important biomarker of bone metabolism, bone gamma-carboxyglutamate protein (BGP). To overcome the agglomeration of graphene and introduce a biocompatible matrix with functional amino groups, CS-G is prepared and modified on the supporting glassy carbon electrode (GCE). Then, AuNPs are electrodeposited on CS-G through their interaction between amine groups of CS. The immobilized AuNPs provide numerous binding sites to immobilize anti-BGP antibodies (Ab_BGP). The specific recognition between BGP and Ab_BGP results in a reduction in the mass transfer of the electrochemical probe (Fe(CN)₆^3-/4-) in solution, leading to a reduced electrochemical signal. Based on this mechanism, fast and ultrasensitive electrochemical detection of BGP is achieved when the concentration of BGP ranges from 100 ag ml⁻¹ to 10 μg mL⁻¹ with a limit of detection (LOD) of 20 ag ml⁻¹ (S/N = 3). The determination of BGP in human serum is also realized with high reliability.

Use of Cysteamine and Glutaraldehyde Chemicals for Robust Functionalization of Substrates with Protein Biomarkers—An Overview on the Construction of Biosensors with Different Transductions

Currently, several biosensors are reported to confirm the absence/presence of an abnormal level of specific human biomarkers in research laboratories. Unfortunately, public marketing and/or pharmacy accessibility are not yet possible for many bodily fluid biomarkers. The questions are numerous, starting from the preparation of the substrates, the wet/dry form of recognizing the (bio)ligands, the exposure time, and the choice of the running buffers. In this context, for the first time, the present overview summarizes the pre-functionalization of standard and nanostructured solid/flexible supports with cysteamine (Cys) and glutaraldehyde (GA) chemicals for robust protein immobilization and detection of biomarkers in body fluids (serum, saliva, and urine) using three transductions: piezoelectrical, electrochemical, and optical, respectively. Thus, the reader can easily access and compare step-by-step conjugate protocols published over the past 10 years. In conclusion, Cys/GA chemistry seems widely used for electrochemical sensing applications with different types of recorded signals, either current, potential, or impedance. On the other hand, piezoelectric detection via quartz crystal microbalance (QCM) and optical detection by surface plasmon resonance (LSPR)/surface-enhanced Raman spectroscopy (SERS) are ultrasensitive platforms and very good candidates for the miniaturization of medical devices in the near future.