Copper nanoclusters-enhanced chemiluminescence for folic acid and nitrite detection

Advances in Folic Acid Biosensors and Their Significance in Maternal, Perinatal, and Paediatric Preventive Medicine

Auxotrophic primates like human beings rely on exogenous dietary vitamin B9 supplementation to meet their metabolic demands. Folates play a crucial role in nucleotide synthesis and DNA methylation. Maternal folate deficiency causes several pregnancy-related complications, perinatal defects, and early childhood cognitive impairments. New evidence suggests excess FA is a potential risk factor resulting in unfavourable genomic and epigenomic alterations. Thus, it is essential to revisit the need to consistently monitor maternal folate levels during pregnancy. Yet, to date, no point-of-care folate-monitoring biosensor is commercially available. Here, we critically appraise the advances in folate biosensors to understand the translational gaps in biosensor design. Further, our review sheds light on the potential role of folate biosensors in strengthening maternal, perinatal, and child healthcare.

Carbon quantum dots for fluorescent detection of nitrite: A review

NO₂^- is commonly found in foods and the environment, and excessive intake of NO₂^- poses serious hazards to human health. Thus, rapid and accurate assay of NO₂^- is of considerable significance. Traditional instrumental approaches for detection of NO₂^- faced with limitations of expensive instruments and complicated operations. Current gold standards for sensing NO₂^- are Griess assay and 2,3-diaminonaphthalene assay, which suffer from slow detection kinetics and bad water solubility. The newly emerged carbon quantum dots (CQDs) exhibit integrated merits including easy fabrication, low-cost, high quantum yield, excellent photostability, tunable emission behavior, good water solubility and low toxicity, which make CQDs be widely applied to fluorescent assay of NO₂^-. In this review, synthetic strategies of CQDs are briefly presented. Advances of CQDs for fluorescent detection of NO₂^- are systematically highlighted. Lastly, the challenges and perspectives in the field are discussed.

A fluorescent carbon dots synthesized at room temperature for automatic determination of nitrite in Sichuan pickles

In this paper, highly fluorescent carbon dots were synthesized from sodium ascorbate and polyethyleneimine at room temperature (R-CDs). The proposed green synthesis method was energy-saving, environmentally friendly and easy online. R-CDs exhibit an optimal emission peak of 490 nm under excitation at 380 nm with a quantum yield of 32 %. R-CDs morphology, composition, and properties were characterized using TEM, FTIR, XPS, UV-vis and fluorescence spectroscopy. The study revealed that nitrite quenched the fluorescence of R-CDs under acidic conditions. Subsequently, this discovered reaction of R-CDs and nitrite was combined with flow-injection technology, and a simple, precise and automatic fluorescence strategy for nitrite determination was accomplished. The response to nitrite was linear in 5-300 μg·L^-1 concentration range and the limit of detection was 2.85 μg·L^-1 (3.3 S/k). This method was applied to nitrite determination in Sichuan pickles during the pickling process and results were consistent with the standard method, demonstrating its feasibility in practical applications.

A turn-on fluorescent nano-probe base on methanobactin-AuNPs for simple and efficient detection of nitrite

Nitrite ions are important markers threatening humans and environmental security. A highly selective method for rapid detection of nitrite needs to be developed. Herein, a novel and rapid fluorescence method for nitrite determination is established on the basis of diazotization-coupling reaction of methanobactin (Mb) extracted by Methylosinus trichosporium OB3b with nitrite on the fluorescence. In the presence of gold nanoparticles (AuNPs), the fluorescence of AuNPs was strongly quenched by the Mb because the sulfhydryl or amino structures on the surface of Mb could be bound to the surface of AuNPs by forming Au-S or Au-N bonds. Upon addition of nitrite, the Mb easily reacts with nitrite to form azo products in the acidic medium. Then, with the increase of nitrite concentration, the Mb-AuNPs fluorescence was gradually recovered, realizing the turn-on fluorescence sensing of nitrite. Under optimal conditions, the proposed method has a good linear relationship with nitrite concentration in the range of 0-8.0 μM and 8.0-50.0 μM, and the detection limit is 16.21 nM. In addition, satisfactory results were obtained for nitrite analysis using milk, ham sausage and leaf mustard as real samples, which demonstrated that the method as-developed would have great practical application prospects.

Doped Carbon Quantum Dots/PVA Nanocomposite as a Platform to Sense Nitrite Ions in Meat

A sensor device based on doped-carbon quantum dots is proposed herein for detection of nitrite in meat products by fluorescence quenching. For the sensing platform, carbon quantum dots doped with boron and functionalized with nitrogen (B,N-Cdot) were synthesized with an excellent 44.3% quantum yield via a one-step hydrothermal route using citric acid, boric acid, and branched polyethylenimine as carbon, boron, and nitrogen sources, respectively. After investigation of their chemical structure and fluorescent properties, the B,N-Cdot at aqueous suspensions showed high selectivity for NO₂^- in a linear range from 20 to 50 mmol L^-1 under optimum conditions at pH 7.4 and a 340 nm excitation. Furthermore, the prepared B,N-Cdots successfully detected NO₂^- in a real meat sample with recovery of 91.4-104% within the analyzed range. In this manner, a B,N-Cdot/PVA nanocomposite film with blue emission under excitation at 360 nm was prepared, and a first assay detection of NO₂^- in meat products was tested using a smartphone application. The potential application of the newly developed sensing device containing a highly fluorescent probe should aid in the development of a rapid and inexpensive strategy for NO₂^- detection.

Bionic Enzyme-Assisted Ion-Selective Amperometric Biosensor Based on 3D Porous Conductive Matrix for Point-of-Care Nitrite Testing

Nitrite plays a critical role in a variety of physiological processes and maintaining the nitrite level in an appropriate range is vital to keep healthy. Current nitrite analysis methods lack sensitivity and require tedious operations, which could not meet the need of point-of-care (POC) nitrite detection in precision medicine. Here we present a cyanocobalamin (VB₁₂) bionic enzyme-assisted ion-selective amperometric biosensor based on 3D porous conductive matrix (PCM), which can facilitate rapid and accurate POC nitrite monitoring in complex biofluids. The experimental findings quantitatively demonstrate that the biosensor has a sensitivity of 64.08 μA/(mM·cm²), a wide linear range of 0.025-45 mM, and low limit of detection of 1 nM. Moreover, the developed VB₁₂/BSA-PCM biosensor shows outstanding stability after 21 days with 2% decline in current signal, and high repeatability between batches with RSD of only 1.29%. Real salivary nitrite detection has been evaluated, and the results match well with the commercial nitrite analyzer. Thus, the bionic enzyme-assisted ion-selective amperometric biosensor proposed herein has potential utility as an affordable tool for POC detection and home-based healthcare.

Gold Nanomaterials and their Composites as Electrochemical Sensing Platforms for Nitrite Detection

Nitrite is one of the abundant toxic components existing in the environment and is likely to have a great potential to affect human health badly. For that reason, it has become crucial to build a reliable nitrite detection method. In recent years, several nitrite monitoring systems have been proposed. Compared with traditional analytical strategies, the electrochemical approach has a bunch of advantages, including low cost, rapid response, easy operation, simplicity, etc. In this case, noble metal nanomaterials, especially Au-based nanomaterials, have attracted attention in electrode modification because of higher catalytic activity, facile mass transfer, and broad active area for determining nitrite. This review is based on the state-of-the-art, which includes a variety of nanomaterials that have been coupled with AuNPs for the creation of nanocomposites, and the construction as well as development of electrochemical sensors for nitrite detection over the last few years (2016-2022). A background study on synthesizing different morphological AuNPs and nanocomposites has also been introduced. The fabrication methods and sensing capabilities of modified electrodes are given special consideration.

Synthesis of Copper Nanoclusters and Their Application for Environmental Pollutant Probes: A Review

Copper nanoclusters (CuNCs) as a new type of probe for environmental contaminants are gaining increasing attention because of its low cost, superior water dispersibility, wide availability and excellent optical properties. Compared with the other probes such as quantum dots and organic dyes, CuNCs show much more potential in practical application for their excellent photostability, large Stokes shift, low toxicity and other preponderance, especially in the fields of biosensing and environmental monitoring. Recently, the template-assisted synthesis of metal nanoclusters (MNCs) has been widely studied. A variety of templates such as proteins, small thiol molecules, polymers, and DNA with different spatial configuration have been used for the preparation of MNCs so far. This review primarily described recent advances in CuNCs in terms of the synthesis of CuNCs from different templates, the methods to improve the fluorescence (FL) properties of CuNCs, as well as the basic detection mechanisms based on the FL properties or catalytic properties. Finally, to promote the practical application of CuNCs probes, the challenges and prospects of CuNCs multifunctional probes are also discussed.

Electrochemical Sensing of Nitrite Ions Using Modified Electrode by Poly 1,8-Diaminonaphthalene/Functionalized Multi-Walled Carbon Nanotubes

A novel electrochemical sensor based on conducting polymer and multi-walled carbon nanotubes was reported for the detection of nitrite ions (NO₂⁻). The hybrid material poly 1,8-Diaminonaphthalene (poly 1,8-DAN)/functionalized multi-walled carbon nanotubes (f-MWCNT) was prepared by using a simple electrochemical approach which is based on the deposition of functionalized multi-walled carbon nanotubes (f-MWCNT) on the surface of the electrode followed by the electropolymerization of 1,8-DAN using cyclic voltammetry. The morphology and the electro-catalytic properties of the obtained electrodes were investigated with Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), Cyclic Voltammetry (CV), and Electrochemical Impedance Spectroscopy (EIS) showing an improvement of the electronic transfer due to the synergic effect between the proprieties of poly 1,8-DAN and f-MWCNT. Under the optimum experimental conditions, the poly 1,8-DAN/f-MWCNT/CPE exhibited excellent electro-catalytic activity towards nitrite detection. The nitrite anodic peak potential decreased by 210 mV compared to the bare carbon paste electrode. The calibration plot of nitrite detection was linear in the range of concentration from 300 to 6500 nM with a low detection limit of 75 nM.

Enhanced Nitrite Detection by a Carbon Screen Printed Electrode Modified with Photochemically-Made AuNPs

Excessive nitrite amounts harm the environment and put public health at high risk. Therefore, accurate and sensitive detection of nitrite in surface and groundwater is mandatory for mitigating its adverse effects. Herein, a highly sensitive electrochemical sensor based on carbon screen-printed electrodes (CSPE) surface-modified with photochemically-made gold nanoparticles (AuNPs, ~12 nm) is proposed for nitrite detection. Scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy show that AuNPs uniformly coat the CSPE, increase its surface area, and contribute to oxidizing nitrite to much lower potential (+0.5 V vs. Ag/AgCl) and faster rate. Under optimized differential pulse voltammetry conditions, the CSPE/AuNPs-PEI electrode responds linearly (R2 > 0.99) to nitrite within a wide concentration range (0.01–4.0 µM), showing a sensitivity of 0.85 µA·µM−1·cm−2 and limit of detection as low as 2.5 nM. The CSPE/AuNPs-PEI electrode successfully detects nitrite in tap water and canned water of olives, showing no influence of those matrices. In addition, the electrode’s response is highly reproducible since a relative standard deviation lower than 10% is observed when the same electrode is operated in five consecutive measurements or when electrodes of different fabrication batches are evaluated.

A red luminescent europium metal organic framework (Eu-MOF) integrated with a paper strip using smartphone visual detection for determination of folic acid in pharmaceutical formulations

Integration of smartphone with visual-based paper strip as a low-cost, fast, and reliable probe for semi-quantitative analysis of folic acid.

Cyanine dye-assembled composite upconversion nanoparticles for the sensing and cell imaging of nitrite based on a single particle imaging method

An upconversion luminescence total internal reflection single particle imaging method was developed for the sensing and cell imaging of nitrite.

A novel ratiometric and colorimetric probe for rapid and ultrasensitive detection of nitrite in water based on an Acenaphtho[1,2-d] imidazole derivative

The concentration of nitrite (NO₂^-) ions above allowable limits in water resources and food stuffs is considered hazardous and has been proven to be of great threat to the environment and public health. In this work, an acenaphtho [1,2-d] imidazole derivative (1) as a ratiometric colorimetric probe is developed. UV-Vis experiments demonstrate that the probe 1 shows excellent selectivity toward NO₂^- in the presence of other potential interfering species, a rapid response (20 s) and a low detection limit (100 nM) by a distinct visual color change with a bathochromic shift of 120 nm from colorless to intense yellow. Besides, this probe is further used for the quantification of nitrite ions in environmental water resources such as tap water, underground water, and surface water samples. The high recoveries (96-99% with relative standard deviations (RSD) of <2.0%) make the probe 1 a promising candidate for practical applications in daily life in the detection of nitrite ions.

Copper nanoclusters: designed synthesis, structural diversity, and multiplatform applications

Atomically precise metal nanoclusters (MNCs) have gained tremendous research interest in recent years due to their extraordinary properties. The molecular-like properties that originate from the quantized electronic states provide novel opportunities for the construction of unique nanomaterials possessing rich molecular-like absorption, luminescence, and magnetic properties. The field of monolayer-protected metal nanoclusters, especially copper, with well-defined molecular structures and compositions, is relatively new, about two to three decades old. Nevertheless, the massive progress in the field illustrates the importance of such nanoobjects as promising materials for various applications. In this respect, nanocluster-based catalysts have become very popular, showing high efficiencies and activities for the catalytic conversion of chemical compounds. Biomedical applications of clusters are an active research field aimed at finding better fluorescent contrast agents, therapeutic pharmaceuticals for the treatment and prevention of diseases, the early diagnosis of cancers and other potent diseases, especially at early stages. A huge library of structures and the compositions of copper nanoclusters (CuNCs) with atomic precisions have already been discovered during last few decades; however, there are many concerns to be addressed and questions to be answered. Hopefully, in future, with the combined efforts of material scientists, inorganic chemists, and computational scientists, a thorough understanding of the unique molecular-like properties of metal nanoclusters will be achieved. This, on the other hand, will allow the interdisciplinary researchers to design novel catalysts, biosensors, or therapeutic agents using highly structured, atomically precise, and stable CuNCs. Thus, we hope this review will guide the reader through the field of CuNCs, while discussing the main achievements and improvements, along with challenges and drawbacks that one needs to face and overcome.

Recent Advances in Electrochemiluminescence and Chemiluminescence of Metal Nanoclusters

Metal nanoclusters (NCs), including Au, Ag, Cu, Pt, Ni and alloy NCs, have become more and more popular sensor probes with good solubility, biocompatibility, size-dependent luminescence and catalysis. The development of electrochemiluminescent (ECL) and chemiluminescent (CL) analytical methods based on various metal NCs have become research hotspots. To improve ECL and CL performances, many strategies are proposed, from metal core to ligand, from intermolecular electron transfer to intramolecular electron transfer. Combined with a variety of amplification technology, i.e., nanostructure-based enhancement and biological signal amplification, highly sensitive ECL and CL analytical methods are developed. We have summarized the research progresses since 2016. Also, we discuss the current challenges and perspectives on the development of this area.

Amino group decorated coordination polymers for enhanced detection of folic acid

A series of fluorescent coordination polymers (CPs) {[Cd₂(CH₃-bpeb)₂(BDC)₂] CP1, (BDC)_0.5/(NH₂-BDC)_0.5-CP1, (BDC)_0.34/(NH₂-BDC)_0.66-CP1, (BDC)_0.25/(NH₂-BDC)_0.75-CP1, (BDC)_0.2/(NH₂-BDC)_0.8-CP1, (NH₂-BDC)-CP1} were prepared from conjugated ligand 4,4'-((2-methyl-1,4-phenylene)bis(ethene-2,1-diyl))bipyridine (CH₃-bpeb), terephthalic acid (BDC), aminoterephthalic acid (NH₂-BDC) and CdSO₄ under solvothermal conditions. The fluorescence of aqueous suspensions of these CPs was quenched by folic acid (FA) in a concentration dependent manner. The efficiency of quenching increasing with an increased proportion of NH₂-BDC ligand in the CP with (NH₂-BDC)-CP1 exhibiting a low detection limit of 1.7 × 10^-7 M.

Facile Synthesis of Ultrastable Fluorescent Copper Nanoclusters and Their Cellular Imaging Application

Copper nanoclusters (Cu NCs) are generally formed by several to dozens of atoms. Because of wide range of raw materials and cheap prices, Cu NCs have attracted scientists’ special attention. However, Cu NCs tend to undergo oxidation easily. Thus, there is a dire need to develop a synthetic protocol for preparing fluorescent Cu NCs with high QY and better stability. Herein, we report a one-step method for preparing stable blue-green fluorescent copper nanoclusters using glutathione (GSH) as both a reducing agent and a stabilizing agent. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and electrospray ionization mass spectrometer (ESI-MS) were used to characterize the resulting Cu NCs. The as-prepared Cu NCs@GSH possess an ultrasmall size (2.3 ± 0.4 nm), blue-green fluorescence with decent quantum yield (6.2%) and good stability. MTT results clearly suggest that the Cu NCs@GSH are biocompatible. After incubated with EB-labeled HEK293T cells, the Cu NCs mainly accumulated in nuclei of the cells, suggesting that the as-prepared Cu NCs could potentially be used as the fluorescent probe for applications in cellular imaging.

Fluorometric assay of iron(II) lactate hydrate and ammonium ferric citrate in food and medicine based on poly(sodium-p-styrenesulfonate)-enhanced Ag nanoclusters

Poly(sodium-p-styrenesulfonate)-enhanced and D-penicillamine stabilized Ag nanoclusters (PSS-DPA-AgNCs) were prepared using one-step ultraviolet irradiation combined with microwave heating method, and the effects of the AgNCs photo-luminescence performance based on different types of polyelectrolytes and energy suppliers were studied detailedly. The as-prepared AgNCs can be used as a viable fluorescent probe for monitoring indirectly iron(II) lactate hydrate (ILH) and ammonium ferric citrate (AFC), respectively. The fluorescence (FL) quenching of PSS-DPA-AgNCs by Fe³⁺ (it is obtained from oxidized ILH/ionized AFC) mainly derives from a dynamic quenching process. Excellent linear relationships exist between the FL quenching degree of the AgNCs and the concentrations of ILH/AFC in the range of 0.17-6.00/0.067-3.33 μmol·L^-1, and corresponding limit of detection (at 3σ/slope) is 12.4/6.04 nmol·L^-1. Moreover, the AgNCs probe was extended to the assays of ILH in tablets, solid beverage or ILH additive and AFC in two kinds of edible salts or syrup with satisfactory results compared with the standard 1, 10-phenanthroline method. In addition, the AgNCs probe reveals a good temperature sensing capability.