A 4D printed nanoengineered super bioactive hydrogel scaffold with programmable deformation for potential bifurcated vascular channel construction.

Four-dimensional (4D) printing of hydrogels enabled the fabrication of complex scaffold geometries out of static parts. Although current 4D fabrication strategies are promising for creating vascular parts such as tubes, developing branched networks or tubular junctions is still challenging. Here, for the first time, a 4D printing approach is employed to fabricate T-shaped perfusable bifurcation using an extrusion-based multi-material 3D printing process. An alginate/methylcellulose-based dual-component hydrogel system (with defined swelling behavior) is nanoengineered with carbonized alginate (∼100 nm) to introduce anti-oxidative, anti-inflammatory, and anti-thrombotic properties and shape-shifting properties. A computational model to predict shape deformations in the printed hydrogels with defined infill angles was designed and further validated experimentally. Shape deformations of the 3D-printed flat sheets were achieved by ionic cross-linking. An undisrupted perfusion of a dye solution through a T-junction with minimal leakage mimicking blood flow through vessels is also demonstrated. Moreover, human umbilical vein endothelial and fibroblast cells seeded with printed constructs show intact morphology and excellent cell viability. Overall, the developed strategy paves the way for manufacturing self-actuated vascular bifurcations with remarkable anti-thrombotic properties to potentially treat coronary artery diseases.

Cheminformatics approach to identify andrographolide derivatives as dual inhibitors of methyltransferases (nsp14 and nsp16) of SARS-CoV-2.

The Covid-19 pandemic outbreak has accelerated tremendous efforts to discover a therapeutic strategy that targets severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to control viral infection. Various viral proteins have been identified as potential drug targets, however, to date, no specific therapeutic cure is available against the SARS-CoV-2. To address this issue, the present work reports a systematic cheminformatic approach to identify the potent andrographolide derivatives that can target methyltransferases of SARS-CoV-2, i.e. nsp14 and nsp16 which are crucial for the replication of the virus and host immune evasion. A consensus of cheminformatics methodologies including virtual screening, molecular docking, ADMET profiling, molecular dynamics simulations, free-energy landscape analysis, molecular mechanics generalized born surface area (MM-GBSA), and density functional theory (DFT) was utilized. Our study reveals two new andrographolide derivatives (PubChem CID: 2734589 and 138968421) as natural bioactive molecules that can form stable complexes with both proteins via hydrophobic interactions, hydrogen bonds and electrostatic interactions. The toxicity analysis predicts class four toxicity for both compounds with LD50 value in the range of 500-700 mg/kg. MD simulation reveals the stable formation of the complex for both the compounds and their average trajectory values were found to be lower than the control inhibitor and protein alone. MMGBSA analysis corroborates the MD simulation result and showed the lowest energy for the compounds 2734589 and 138968421. The DFT and MEP analysis also predicts the better reactivity and stability of both the hit compounds. Overall, both andrographolide derivatives exhibit good potential as potent inhibitors for both nsp14 and nsp16 proteins, however, in-vitro and in vivo assessment would be required to prove their efficacy and safety in clinical settings. Moreover, the drug discovery strategy aiming at the dual target approach might serve as a useful model for inventing novel drug molecules for various other diseases.

Polymeric optical fiber biosensor with PAMAM dendrimer-based surface modification and PlGF detection for pre-eclampsia diagnosis.

Pre-eclampsia (PE) is a life-threatening complication that occurs during pregnancy, affecting a large number of pregnant women and newborns worldwide. Rapid, on-site and affordable screening of PE at an early stage is necessary to ensure timely treatment and minimize both maternal and neonatal morbidity and mortality rates. Placental growth factor (PlGF) is an angiogenic blood biomarker used for PE diagnosis. Herein, we report the plasmonic fiber optic absorbance biosensor (P-FAB) strategy for detecting PlGF at femtomolar concentration using polymethyl methacrylate (PMMA) based U-bent polymeric optical fiber (POF) sensor probes. A novel poly(amidoamine) (PAMAM) dendrimer based PMMA surface modification is established to obtain a greater immobilization of the bioreceptors compared to a linear molecule like hexamethylenediamine (HMDA). Plasmonic sandwich immunoassay was realized by immobilizing the mouse anti-PlGF (3H1) on the U-bent POF sensor probe surface and gold nanoparticles (AuNP) labels conjugated with mouse anti-PlGF (6H9). The POF sensor probes could measure PlGF within 30 min using the P-FAB strategy. The limit-of-detection (LoD) was found to be 0.19 pg/mL and 0.57 pg/mL in phosphate-buffered saline and 10× diluted serum, respectively. The clinical sample testing, with eleven positive and eleven negative preeclamptic pregnancy samples, successfully confirmed the accuracy, reliability, specificity, and sensitivity of the P-FAB based POF sensor platform, thereby paving the way for cost-effective technology for PlGF detection and its potential for pre-eclampsia diagnosis.

Integrated molecular and quantum mechanical approach to identify novel potent natural bioactive compound against 2'-O-methyltransferase (nsp16) of SARS-CoV-2.

With the advent of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) outbreak, efforts are still in progress to find out a functional cure for the infection. Among the various protein targets, nsp16 capping protein is one of the vital targets for drug development as it protects the virus against the host cell nucleases and evading innate immunity. The nsp16 protein forms a heterodimer with a co-factor nsp10 and triggers 2'-O-methyltransferase activity which catalyzes the conversion of S-adenosyl methionine into S-adenosyl homocysteine. The free methyl group is transferred to the 2'-O position on ribose sugar at the 5' end of mRNA to form the cap-1 structure which is essential for replication of the virus and evading the innate immunity of the host. In this study, we identify a potential lead natural bioactive compound against nsp16 protein by systematic cheminformatic analysis of more than 144k natural compounds. Virtual screening, molecular docking interactions, ADMET profiling, molecular dynamics (MD) simulations, molecular mechanics-generalized born surface area (MM-GBSA), free energy analysis and density functional theory analysis were used to discover the potential lead compound. Our investigation revealed that ZINC8952607 (methyl-[(6-methyl-2,3,4,9-tetrahydro-1H-carbazol-1-yl)aminomethyl]BLAHone) has the greatest binding affinity and best pharmacokinetic parameters due to presence of carbazol and BLAHone (biaryl moiety). Further, time-dependent MD simulation analysis substantiates the stability and rigidness of nsp16 protein even after interaction with the lead compound. We believe that the compound ZINC8952607 might establish as a novel natural drug candidate against CoVID-19 infection.Communicated by Ramaswamy H. Sarma.

Plasmonic nanoparticle etching-based optical sensors: current status and future prospects.

Plasmonic nanoparticles are an emerging tool for developing label-free multicolorimetric sensors for biosensing and chemosensing applications. The color absorbed by nanoparticles from visible light is influenced by their size, shape, orientation, and interparticle distance. Differently sized and shaped gold and silver nanoparticles exhibit a wide range of colors, aiding in the development of label-free sensors. Etching is the process of oxidizing nanoparticles, which alters their aspect ratio, shape, plasmonic peak, and outward appearance. It is typically used to create sensitive sensing platforms. Through etching, analytes could be detected in a simple, sensitive, and selective manner. The multicolor readout of nanoparticle etching-based multicolorimetric sensors can overcome the limitations of conventional colorimetric assays and improve the accuracy of visual inspection. This review discusses different approaches for target sensing using nanoparticle etching strategies like direct etching, enzyme-mediated etching, chemical reaction-driven etching, and anti-etching-based sensors and their mechanisms. In the future, etching strategies could be modified into portable sensing devices to detect a variety of analytes, which will aid in the development of on-time, in situ, and point-of-care sensing systems.

Repurposing the in-house generated Alzheimer's disease targeting molecules through computational and preliminary in-vitro studies for the management of SARS-coronavirus-2.

Covid-19 was declared a world pandemic. Recent studies demonstrated that Covid-19 impairs CNS activity by crossing the blood-brain barrier and ensuing cognitive impairment. In this study, we have utilized Covid-19 main protease (Mpro) as a biological target to repurpose our previously reported multifunctional compounds targeting Alzheimer's disease. Molecular docking, spatial orientation, molecular dynamics simulation, MM-GBSA energy calculation, and DFT studies were carried out with these molecules. Among all the compounds, F27, F44, and F56 exhibited higher binding energy (- 8.03, - 8.65, and - 8.68 kcal/mol, respectively) over the co-crystal ligand O6K (- 7.00 kcal/mol). In MD simulation, compounds F27, F44, and F56 could make a stable complex with Mpro target throughout the simulation. The compounds were synthesized following reported methods and subjected for cytotoxicity, and assessment of their capability to cross the blood-brain barrier in PAMPA assay, and antioxidant property evaluation through DPPH assay. The compounds F27, F44, and F56 exhibited cytocompatibility with the SiHA cell line and also displayed significant antioxidant properties with IC50 = 45.80 ± 0.27 µM, 44.42 ± 0.30 µM, and 42.74 ± 0.23 µM respectively. In the PAMPA assays, the permeability coefficient (Pe) value of F27, F44, and F56 lies in the acceptable range (Pe > 4). The results of the computational and preliminary in-vitro studies strongly corroborate the potential of F27, F44, and F56 as a lead for further optimization in treating the CNS complications associated with Covid-19.

Extraction, isolation, synthesis, and biological evaluation of novel piperic acid derivatives for the treatment of Alzheimer's disease.

In this paper, we developed a series of piperic acid (PA) analogs with the aim of overcoming the limitations associated with the natural products for the management of Alzheimer's disease (AD). A comprehensive SAR study was performed to enhance cholinesterase inhibition of PA. The acetylcholinesterase inhibition and its kinetic data suggested 6j as the lead molecule (AChE IC50 = 2.13 ± 0.015 µM, BChE = 28.19 ± 0.20%), in comparison to PA (AChE = 7.14 ± 0.98%) which was further selected for various biological studies in AD models. 6j, exhibited interaction with the peripheral anionic site of AChE, BBB permeability (Pe = 7.98), and antioxidant property (% radical scavenging activity = 35.41 ± 1.09, 2.43 ± 1.65, for 6j and PA at 20 M[Formula: see text], respectively). The result from the metal chelation study suggests that 6j did not effectively chelate iron. The molecular modeling studies suggested that 6j could effectively interact with Ser293, Phe295, Arg296, and Tyr34 of AChE. In the cell-based cytotoxicity studies, 6j exhibited cytocompatibility at the different tested concentrations. The acute toxicity data on mice suggested that compound 6j had no renal and hepatotoxicity at 500 mg/kg. Moreover, 6j could effectively reverse scopolamine-induced amnesia by improving spatial and cognitive memory in mice. The above results strongly suggest that compound 6j may act as a novel multi-targeted lead for AD therapy.

Discovery of andrographolide hit analog as a potent cyclooxygenase-2 inhibitor through consensus MD-simulation, electrostatic potential energy simulation and ligand efficiency metrics.

Cyclooxygenase-2 (COX-2) is the key enzyme responsible for the conversion of arachidonic acid to prostaglandins that display pro-inflammatory properties and thus, it is a potential target protein to develop anti-inflammatory drugs. In this study, chemical and bio-informatics approaches have been employed to find a novel potent andrographolide (AGP) analog as a COX-2 inhibitor having better pharmacological properties than aspirin and rofecoxib (controls). The full amino acid sequenced human Alpha fold (AF) COX-2 protein (604AA) was selected and validated for its accuracy against the reported COX-2 protein structures (PDB ID: 5F19, 5KIR, 5F1A, 5IKQ and 1V0X) followed by multiple sequence alignment analysis to establish the sequence conservation. The systematic virtual screening of 237 AGP analogs against AF-COX-2 protein yielded 22 lead compounds based on the binding energy score (< - 8.0 kcal/mol). These were further screened out to 7 analogs by molecular docking analysis and investigated further for ADMET prediction, ligand efficiency metrics calculations, quantum mechanical analysis, MD simulation, electrostatic potential energy (EPE) docking simulation, and MM/GBSA. In-depth analysis revealed that AGP analog A3 (3-[2-[(1R,4aR,5R,6R,8aR)-6-hydroxy-5,6,8a-trimethyl-2-methylidene-3,4,4a,5,7,8-hexahydro-1H-naphthalen-1-yl]ethylidene]-4-hydroxyoxolan-2-one) forms the most stable complex with the AF-COX-2 showing the least RMSD value (0.37 ± 0.03 nm), a good number of hydrogen bonds (protein-ligand H-bond = 11, and protein H-bond = 525), minimum EPE score (- 53.81 kcal/mol), and lowest MM-GBSA before and after simulation (- 55.37 and - 56.25 kcal/mol, respectively) value compared to other analogs and controls. Thus, we suggest that the identified A3 AGP analog could be developed as a promising plant-based anti-inflammatory drug by inhibiting COX-2.

Shape dependent sensing potential of gold nanoparticles in etching based multicolorimetric plasmonic-ELISA.

In the present study, a systematic investigation has been carried out for the first time to assess the potential of three different shapes of gold nanoparticles (AuNPs), viz. nanorods (AuNRs), nanotriangles (AuNTs), and nanospheres (AuNSs), to develop a horseradish peroxidase (HRP) enzyme-mediated etching-based plasmonic ELISA (p-ELISA) strategy. The etching of the AuNPs in ELISA is achieved by 3'-3-5'-5-tetramethylbenzidine (TMB2+), which is produced by the biocatalytic conversion of chromogenic TMB via HRP. All three types of AuNPs were interacted with varying concentrations of TMB2+ (7-131 µM) (product of HRP enzyme reaction) and characterized for visible color change and by UV-Vis spectroscopy and transmission electron microscopy (TEM). From the comparative analysis of all three shapes of AuNPs, AuNRs exhibited vivid visible color change and absorbance intensity change compared to spherical and triangle-shaped nanoparticles. The TEM analysis of the etched nanoparticles revealed the gradual etching pattern of AuNRs compared to AuNTs which resulted in multicolor generation as opposed to AuNTs where the etching was relatively very fast and thus shows a faster shape transformation and poor color discrimination. Further, the potential of the AuNR etching-based optimized strategy was successfully demonstrated to develop an indirect competitive p-ELISA for human IgG detection. The developed p-ELISA showed an ultra-low visual limit of detection of 1 fg mL-1 (∼6.54 aM) without the aid of any sophisticated instruments. In the future, the developed competitive p-ELISA strategy can be easily employed to develop cost-effective, portable, and point-of-care assays for the detection of various disease biomarkers with ultra-high sensitivity.

Enzyme-assisted metal nanoparticles etching based plasmonic ELISA: Progress and insights.

The unique size and shape tunable localized surface plasmon resonance (LSPR) properties of the noble metal nanoparticle have been extensively exploited to realize a variety of enzyme-based optical biosensors. Although approaches like metal film deposition, nanoparticle aggregation, and synthesis & growth of metal nanoparticles are quite useful, metal nanoparticle etching-based biosensors offer greater sensitivity, selectivity, and stability against various environmental factors which makes this strategy easy to use for field applications. This review discusses the current state-of-art of plasmonic nanoparticle etching-based enzyme-linked immunosorbent assay (ELISA) realized for visual detection of various analytes. The naked eye detection, i.e. without any optical readout device, is the additional advantage of this sensing approach that reduces the analysis cost significantly making it feasible under resource-constrained settings. This review paper provides deeper insights into biocatalytic etching mechanisms of various plasmonic nanoparticles resulting in vivid color change as a function of analyte concentration. Although nanoparticle etching-based ELISA has huge potential, steps need to be taken to realize a point-of-care (POC) nanodiagnostic before its translation to a commercial technique or product that can be achieved in near future by integrating it with microfluidics technology and other technological avenues.

Emerging trends in point-of-care sensors for illicit drugs analysis.

Consumption of illicit narcotic drugs and fatal or criminal activities under their influence has become an utmost concern worldwide. These drugs influence an individual's feelings, perceptions, and emotions by altering the state of consciousness and thus can result in serious safety breaches at critical workplaces. Point-of-care drug-testing devices have become the need-of-the-hour for many sections such as the law enforcement agencies, the workplaces, etc. for safety and security. This review focuses on the recent progress on various electrochemical and optical nanosensors developed for the analysis of the most common illicit drugs (or their metabolites) such as tetrahydrocannabinol (THC), cocaine (COC), opioids (OPs), amphetamines & methamphetamine, and benzodiazepine (BZDs). The paper also highlights the sensitivity and selectivity of various sensing modalities along with evolving parameters such as real-time monitoring and measurement via a smart user interface. An overall outlook of recent technological advances in point of care (POC) devices and guided insights and directions for future research is presented.

Plasmonic Fiberoptic Absorbance Biosensor (P-FAB) for Rapid Detection of SARS-CoV-2 Nucleocapsid Protein.

SARS-CoV-2 nucleocapsid protein-based COVID-19 diagnosis is a promising alternative to the high-priced, time-consuming, and labor-intensive RT-PCR tests. Here, we developed a rapid, dip-type, wash-free plasmonic fiber optic absorbance biosensor (P-FAB) strategy for the point-of-care detection of SARS-CoV-2 N-protein, expressed abundantly during the infection. P-FAB involves a sandwich assay with plasmonic labels on the surface of a U-bent fiber optic sensor probe with a high evanescent wave absorbance (EWA) sensitivity. The SARS-CoV-2 N-protein is quantified in terms of the change in the intensity of the light propagating through the U-bent sensor probe coupled to a green LED and a photodetector. Firstly, the optical fiber material (silica vs. polymeric optical fiber), was evaluated to realize a sensitive sensor platform. The optimal size of AuNP labels (20, 40, and 60 nm) to achieve high sensitivity and a lower limit of detection (LoD) was investigated. Following the P-FAB strategy, fused silica/glass optical fiber (GOF) U-bent senor probe and citrate-capped AuNP labels (size ~40 nm) gave rise to an LoD down to ~2.5 ng/mL within 10 mins of read-out time. Further, studies on development and validation of a point of care (PoC) read-out device, and preclinical studies are in progress.

The current state of the art of plasmonic nanofibrous mats as SERS substrates: design, fabrication and sensor applications.

Surface-enhanced Raman scattering (SERS) is a widely used analytical tool that allows molecular fingerprint-based ultra-sensitive detection through an enhanced electromagnetic field generated by plasmonic metal nanoparticles (MNPs) by virtue of their localized surface plasmon resonance (LSPR). Although significant progress has been made in the design and fabrication of a variety of SERS substrates, MNP-decorated electrospun nanofibrous (NF) mats have attracted much attention due to their unique nanoscale structural and functional properties. This review focuses on the current state of the art in the fabrication of plasmonic NF mats with the main focus on the pre-mix, in situ, and ex situ approaches. The characteristic functional advantages and limitations of these strategies are also highlighted, which might be helpful for the research community when adopting a suitable approach. The potential of these plasmonic NF mats as a SERS-active optical sensor substrate, and their performance parameters such as the limit of detection, analytical range, and enhancement factor, and real-world applications are also discussed. The summary and futuristic discussion in this review might be of significant value in developing plasmonic NF mat-based SERS-active point-of-care diagnostic chips for a wide range of applications.

Gold Nanoparticle-Redox Ionic Liquid based Nanoconjugated Matrix as a Novel Multifunctional Biosensing Interface.

Creation of interfaces with a prudent design for the immobilization of biomolecules is substantial in the construction of biosensors for real-time monitoring. Herein, an adept biosensing interface was developed using a nanoconjugated matrix and has been employed toward the electrochemical determination of hydrogen peroxide (H2O2). The anionic gold nanoparticle (AuNP) was electrostatically tethered to cationic redox ionic liquid (IL), to which the horseradish peroxidase (HRP) enzyme was covalently immobilized to form a nanobioconjugate. The anthracene-substituted, aldehyde-functionalized redox IL (CHO-AIL) was judiciously designed with the (i) imidazolium cation for electrostatic interaction with AuNPs, (ii) anthracene moiety to mediate the electron transfer, and (iii) free aldehydic group for covalent bonding with a free amine group of the enzyme. Thus, the water-soluble HRP is effectively bonded to the CHO-AIL on a glassy carbon electrode (GCE) via imine bond formation, which resulted in the formation of the HRP-CHO-AIL/GCE. Electrochemical investigations on the HRP-CHO-AIL/GCE reveal highly stable and distinct redox peaks for the anthracene/anthracenium couple at a formal potential (E°') of -0.47 V. Electrostatic tethering of anionic AuNPs to the HRP-CHO-AIL promotes the electron transfer process in the HRP-CHO-AIL/AuNPs/GCE, as observed by the reduction in the formal potential to -0.42 V along with the enhancement in peak currents. The HRP-CHO-AIL/AuNPs/GCE has been explored toward the electrocatalytic detection of H2O2, and the modified electrode demonstrated a linear response toward H2O2 in the concentration range of 0.02-2.77 mM with a detection limit of 3.7 µM. The developed biosensor ascertained predominant selectivity and sensitivity in addition to remarkable stability and reproducibility, corroborating the suitableness of the platform for the effectual biosensing of H2O2. The eminent performance realized with our biosensor setup is ascribed to the multifunctional efficacy of this newly designed nanobioconjugate.

Bimetallic Hollow Nanostructures for Colorimetric Detection of Picomolar Level of Mercury.

In this paper, we report the use of bimetallic hollow nanostructures (BHNS), consisting of gold and silver metals, for colorimetric detection of mercury. The sodium dodecyl sulphate (SDS)-capped BHNS were prepared by galvanic etching of silver nanoparticles (AgNPs) using gold chloride resulting in a partially hollow AgNPs with the gold layer at its surface. These BHNS were interacted with an aqueous solution of mercury ions (Hg2+) in the concentration range of 10 pM-10 mM. Interestingly, at higher concentration range (10 µM-10 mM), a noticeable change in the solution color was observed with a prominent decrease in the absorption intensity and blue-shift in the peak plasmonic wavelength. This could be attributed to (i) complexation reaction between the anionic BHNS (due to the negatively charged SDS capping) and cationic Hg2+ and (ii) oxidative etching of silver from BHNS causing its depletion and resulting into Ag-Hg amalgam and/or aggregation of the nanostructures. In contrast, at lower concentration range (i.e., 10 pM-10 nM), an increase in the absorption intensity was observed, which was possibly due to the oxidative etching of silver from BHNS without aggregation of the nanostructures. The low amount of Hg2+ was not sufficient enough to interact with SDS capping layer present on the BHNS surface, unlike the higher concentrations of mercury and therefore, did not cause any aggregation. The developed colorimetric sensor showed high sensitivity and selectivity towards Hg2+ detection with a limit of detection of 10 pM and good linearity (R² = 0.97) in the concentration range of 10 pM-10 nM.

P-FAB: A Fiber-Optic Biosensor Device for Rapid Detection of COVID-19.

Rapid and low-cost diagnosis of COVID-19 is essential to identify the infected subjects, particularly the asymptomatic cases, primarily to arrest the spread of the disease through local transmission. Antibody-based chromatographic serological tests, as an alternative to RT-PCR, offer only limited help due to high false positives. We propose to exploit our field-deployable/portable plasmonic fiber-optic absorbance biosensor (P-FAB) platform for one-step, wash-free detection of SARS-CoV-2 virus particles directly in saliva sample with minimal sample pre-processing.

Nanomaterials based optical and electrochemical sensing of histamine: Progress and perspectives.

Histamine is known to be a principal causative agent associated with marine food poisoning outbreaks worldwide, which is typically formed in the contaminated food by decarboxylation of histidine by bacterial histidine decarboxylase. Upon quantification of histamine in different food products, one can comment on the quality of the food and use it as an indicator of the good manufacturing practices and the state of preservation. The United States Food and Drug Administration (FDA) has established 50 ppm (50 mg/kg) of histamine as the chemical index for fish spoilage. Consumption of foods containing histamine higher than the permissible limit can cause serious health issues. Several methods have been developed for the determination of histamine in a variety of food products. The conventional methods for histamine detection such as thin layer chromatography, capillary zone electrophoresis, gas chromatography, colorimetry, fluorimetry, ion mobility spectrometry, high-performance liquid chromatography, and enzyme-linked immunosorbent assay (ELISA), are being used for sensitive and selective detection of histamine. However, there are a number of disadvantages associated with the conventional techniques, such as multi-step sample processing and requirement of expensive sophisticated instruments, which restrict their applications at laboratory level only. In order to address the limitations associated with the traditional methods, new approaches have been developed by various research groups. Current advances in nanomaterial-based sensing of histamine in different food products have shown significant measurement accuracy due to their high sensitivity, specificity, field deployability, cost and ease of operation. In this review, we have discussed the development of nanomaterials-based histamine sensing assays/strategies where the detection is based on optical (fluorescence, surface enhanced Raman spectroscopy (SERS), localized surface plasmon resonance) and electrochemical (impedimetric, voltammetry, potentiometric, etc.). Further, the advantages, disadvantages and future scope of the nanomaterials-based histamine sensor research are highlighted.

Dendrimer as a multifunctional capping agent for metal nanoparticles for use in bioimaging, drug delivery and sensor applications.

Advances in nanoparticle research, particularly in the domain of surface-engineered, function-oriented nanoparticles, have had a profound effect in many areas of scientific research and aided in bringing unprecedented developments forward, particularly in the biomedical field. Surface modifiers/capping agents have a direct bearing on the major properties of metal nanoparticles (MNPs), ranging from their physico-chemical properties to their stability and functional applications. Among the different classes of capping agents, dendrimers have gained traction as effective multifunctional capping agents for MNPs due to their unique structural qualities, dendritic effect and polydentate nature. Dendrimer-coated metal nanoparticles (DC-MNPs) are typically produced by both (i) a one-pot strategy, where metal ions are reduced in the presence of dendrimer molecules and (ii) a multi-pot strategy, where a sequence of reactions involving the reduction of metal ions, activation, conjugation and purification steps are involved. These DC-MNPs have shown remarkable ability to stabilize MNPs by means of electrostatic interactions, coordination chemistry or covalent attachment, due to them entailing a large number of sites at which further molecular moieties can be conjugated. This review article is an attempt to consolidate the on-going work, particularly over the last five years, in the field of the synthesis of dendrimer-coated MNPs and their potential applications in bioimaging, drug delivery and biochemical sensors.

Fluorescence Based Study for Melamine Detection Using Gold Colloidal Solutions.

A comparative study on detection of melamine with different sized citrate capped AuNPs namely 15 nm (AuNPs-I), 30 nm (AuNPs-II), and 40 nm (AuNPs-III) was carried out by fluorescence spectroscopy. The AuNPs emitted strong fluorescence at 421 nm with different intensity at 116.122, 220.511 and 253.665 for AuNPs-I, AuNPs-II and AuNPs-III respectively on excitation with 308 nm. On interaction with melamine, the AuNPs aggregated resulting in the enhancement of the fluorescent intensity of AuNPs. The sensitivity of melamine detection was studied for three different sizes of AuNPs by drawing a calibration curve between the concentration of melamine and fluorescence intensity. A good sensitivity was observed for AuNPs-II having the detection limit as low as 0.66 nM (3σ) which was lower in comparison to the detection limit of AuNPs-I (2.78 nM) and AuNPs-III (7.74 nM). The cost of synthesis was low as the usage of HAuCl4 in the synthesis of AuNPs-II was lower compared to the other sizes of AuNPs resulting in low cost of chemicals. The AuNPs-II was further chosen for carrying out selectivity study and for detecting the concentration of melamine. The recovery percentage of melamine in raw milk, liquid milk and milk powder after pre-treatment was found to be 100 %, 97 % to 100 % and 94 % to 99 % respectively.

Emerging use of nanostructure films containing capped gold nanoparticles in biosensors.

The localized surface plasmon resonance (LSPR) property of gold nanoparticles (GNP) has been exploited in a variety of optical sensor configurations including solution-based bioassays, paper-based colorimetric detection, surface-confined nanoparticle film/array-based sensing, etc. Amongst these, gold nanostructured films are of great interest because of their high stability, good reproducibility, robustness, and cost-effectiveness. The inherent optical characteristics of GNP, are attributed to parameters like size and shape (eg, nanospheres, nanorods, nanostars), eg, LSPR spectral location sensitivity to the local environment, composition (eg, gold-silver or silica-gold nanoshells), sensing volume, mesospacing, and multiplexing. These properties allow sensor tunability, enabling enhanced sensitivity and better performance of these biosensors. Ultrasensitive biosensor designs were realized using gold nanostructured films fabricated by bottom-up as well as top-down approaches. In this review, we describe the past, present, and future trends in the development of GNP-LSPR-based sensors, concentrating on both design (fabrication) and application. In the process, we have discussed various combinations of GNP size and shape, substrate, and application domains.