A label-free multicolor colorimetric and fluorescence dual mode biosensing of HIV-1 DNA based on the bifunctional NiFe2O4@UiO-66 nanozyme

Quantifying fluorescence contrast of latent fingerprints developed with micro/nanoparticles through spectroscopic analysis

Fluorescent micro/nanoparticles have been used to visualize latent fingerprints in forensic science. However, due to the current lack of a systematic method to quantify the fluorescence contrast of developed fingerprints, the comparison of fingerprint visualization effects of various developing agents is still limited to empirical evaluation. Here, we presented a fingerprint fluorescence contrast quantification strategy that comprehensively considers fluorescence intensity and color indexes, based on photoluminescence spectroscopy analysis. The intensity index represents the relative fluorescence intensity (I) between the fingerprint and the background. The color index is quantified by its three elements, including hue, saturation, and value (L), where hue and saturation are reflected by chroma (C). Fluorescence contrast is defined as the product of relative fluorescence intensity, chroma parameter, and the common logarithm of value index (I·C·lg L). The proposed approach quantified fingerprints deposited on substrates with varying degrees of patterning and fluorescence interference, using full-color-emitting micro/nanoparticles, and was compared with existing methods, demonstrating its high detection limit, accuracy, and sensitivity. Finally, we developed a tunable multi-color fingerprint enhancement technique to enhance low-quality and low-contrast fingerprints. Therefore, the established comprehensive fluorescence contrast quantification and enhancement strategy provides a new avenue for practical forensic analysis and identification.

A multiplexing immunosensing platform for the simultaneous detection of snake and scorpion venoms: Towards a better management of antidote administration

Envenomation accidents are usually diagnosed at the hospital through signs and symptoms assessment such as short breath, dizziness and vomiting, numbness, swilling, bruising, or bleeding around the affected site. However, this traditional method provides inaccurate diagnosis given the interface between snakebites and scorpion stings symptoms. Therefore, early determination of bites/stings source would help healthcare professionals select the suitable treatment for patients, thus improving envenomation management. In this study, we developed an innovative multiplexing platform based on dual immunosensors for the simultaneous determination of snake and scorpion venoms using a label-free electrochemical platform. The dual immunosensor was fabricated on graphene/gold nanoparticle modified screen-printed electrodes. The electrodes were first modified with two chemical linkers (cysteamine/phenylene diisothiocyanate) to facilitate the immobilization of the antibodies (antivenoms) through covalent binding. The proposed immunosensor was tested with different venoms that specific to six snake species and two scorpion species. The detection was undergone by monitoring the reduction peak current variation after the venom binding using square wave voltammetry, in presence of ferro/ferricyanide redox system. The dual immunosensor enabled a sensitive and selective simultaneous detection of the snake and scorpion species venoms within wide linear ranges in the limits of detection ranging from 0.057 to 0.027 μg/mL. The applicability of the venoms immunosensor has also been evaluated for the detection of snake and scorpion venoms in human serum samples showing high recovery percentages. These achievements show the great potential of our multiplexing approach for the early detection of snake or scorpion envenomation.

In-situ Ti-Ir and ammonium thiocyanate modifiers for improvement of sensitivity of Sc to sub parts per billion levels and its accurate quantification in coal fly ash and red mud by GFAAS

A new analytical method for the determination of scandium at parts per billion levels in an industrial by products such as red mud and coal fly ash has been developed. Current technology developments demand for routine testing of Sc in various samples and for simple methods to use. Graphite furnace atomic absorption spectrometry (GFAAS) meets these requirements, but its detection limit is often too high due to Sc peak tailing problem, likely caused by carbide formation. This issue is resolved, and sensitivity is enhanced, by using permanent, conventional and sulfate-based modifiers and optimizing operational parameters. Maximum sensitivity and optimal peak shape are achieved using a mixed solution of 250 μg each of Ti and Ir, with 1 % ammonium thiocyanate as an in-situ modifier. Sensitivity is further enhanced by an in-situ furnace pre-concentration by multiple injection mode, yielding a detection limit of 0.2 ng mL-1 and a characteristic mass of 11 pg. The method is validated using scandium-based NIST SRM 1633b coal fly ash and spiked recovery studies on coal fly ash and red mud. A rapid leaching procedure for Sc from coal fly ash is optimized. Scandium concentrations obtained via the proposed method are compared with ICP-OES results, showing good agreement. The trueness of the method expressed as the percentage deviation of the method value from the corresponding true value was found to be 4.3 % for determination of Sc in the coal fly ash and 2.1 % for red mud. The relative standard deviation (RSD) is found to be 5 %.

Novel paper sensor with modified aptamer for accurate detection of clinical cardiac troponin I

Accurate and rapid detection of Cardiac Troponin I (CTnI) is essential for the early diagnosis and timely management of myocardial infarction (MI). However, conventional detection methods relying on antigen-antibody interactions often face challenges such as high costs and lengthy procedures. Novel detection methods based on antigen-aptamer interactions offer a potentially superior alternative. Nevertheless, the performance of antigen-aptamer sensors is typically compromised by the unstable structure of aptamers, resulting in limited sensitivity and inconsistent specificity in CTnI detection. To address these issues, we have developed an innovative aptamer structure to construct a paper-based sensor comprising a paper electrode and a CTnI aptamer detection module. The paper electrode employs PEDOT:PSS to uniformly distribute single-walled carbon nanotubes (SWCNTs) at high concentrations on filter paper. The detection module utilizes modified CTnI aptamers with a continuous (AT)5 sequence in the anchor domain to enhance stable immobilization on SWCNTs without chemical reactions. We discovered that incorporating appropriate 18-atom hexa-ethylene glycol spacers (Sp18) between the protein-capture and anchor domains of the aptamers can improve the sensitivity of the current response for CTnI detection. Through the optimization of annealing temperature and duration, the paper sensor Aps3-CTnI-PS@CP, which integrates (AT)5 and three Sp18 into the aptamer, demonstrated enhanced sensitivity and specificity for CTnI detection. When applied to clinical samples, Aps3-CTnI-PS@CP exhibited a favorable receiver operating characteristic (ROC) curve, with an area under the curve (AUC) of 0.982, a sensitivity of 0.917, and a specificity of 0.945 for CTnI detection. This performance correlates strongly with traditional chemiluminescence immunoassay (CLIA) assays used in clinical settings. The straightforward fabrication process and minimal batch-to-batch variability make Aps3-CTnI-PS@CP a promising candidate for clinical aptamer-based CTnI detection.

Self-Powered Glucose Biosensor Based on Non-Enzymatic Biofuel Cells by Au Nanocluster/Pd Nanocube Heterostructure and Fe3C@C-Fe Single-Atom Catalyst

Self-powered biosensors (SPBs) based on biofuel cells (BFCs) use electrical output as a sensing signal without the need of external power supplies, providing a feasible approach to constructing miniaturized implantable or portable devices. In this work, a novel nanozyme of gold nanoclusters/palladium nanocubes (AuNCs/PdNCs) heterostructure is successfully fabricated to develop an innovatively self-powered and non-enzymatic glucose sensing system. The AuNCs/PdNCs with glucose oxidase (GOD)-like activity exhibits superior electrocatalytic and non-enzymatic sensing performance toward glucose. The non-enzymatic BFCs-based SPBs system, established on the AuNCs/PdNCs (anodic catalyst) and single atomic Fe sites coupled with carbon-encapsulated Fe3C crystals (Fe3C@C-Fe SACs as a cathodic catalyst) platform, exhibits an exceptional sensitivity to glucose with 0.151 µW cm-2 mm-1 (3.4 times higher than the PdNCs), outstanding selectivity and robust stability. The outstanding performance of the BFCs-based SPBs system can be attributed to the synergistic cooperation between the PdNCs and AuNCs.

Vertical growth of rhenium disulfide on rGO empowers multi-signal amplification for ultrasensitive MiRNA-21 detection

Unique rhenium disulfide/reduced graphene oxide (ReS2/rGO) nanoframeworks were synthesized with a hierarchical layered and porous structure for the ultrasensitive electrochemical detection of microRNA-21 (miRNA-21) by empowering multi-signal amplification strategy of catalytic hairpin self-assembly-hybridization chain reaction (CHA-HCR). The layered and porous nanostructures endowed ReS2/rGO with a larger specific surface area and more active sites through connecting vertical ReS2 with rGO which was preferable for promoting the electron transfer over electrode surface because of a conductive network. This nanoframework facilitated the loading of adequate gold nanoparticles to fix the capture probe via Au-S bond. In the presence of the target miRNA-21, the CHA-HCR double amplification reaction could be triggered to generate a long double strand with methylene blue (MB) embedded inside. The electrochemical sensing platform was thus empowered by the unique ReS2/rGO nanoframeworks to detect miRNA-21 in the range 1 fM ~ 100 pM with the remarkably enhanced sensitivity through detecting the significantly amplified signal from the REDOX reaction of MB inside the long chain. The verification of the miRNA-21 detection in real blood samples further proved the great potential of this new method with the limit of detection reduced down to 0.057 fM and opens a new window for ReS2 in developing sensitive biosensors for early clinical cancer diagnosis.

A dual-signal biosensor based on surface-enhanced Raman spectroscopy for high-sensitivity quantitative detection and imaging of circRNA in living cells

Circular RNAs (circRNAs) are non-coding RNAs that play key roles in the development and progression of cancer through various mechanisms of action, making them promising biomarkers for cancer diagnosis, prognosis, and treatment. In the present study, a biosensor based on surface-enhanced Raman spectroscopy (SERS) was developed for rapid, simple, and sensitive quantitative detection of intracellular circRNAs for the first time. A dual-signal SERS nanoprobe with a 4MBN and ROX signal molecule was fabricated, and the ROX signal intensity was used to determine the concentration of target circSATB2. 4MBN was used as an internal standard to calibrate the ROX signal, thereby achieving highly sensitive and reliable detection of the target circRNA with a limit of detection of 0.043 pM. Furthermore, the relatively high expression of circSATB2 in lung cancer cells compared to that in normal lung epithelial cells was successfully characterized by the proposed SERS imaging method, which is consistent with the results of standard reverse transcription-polymerase chain reaction (RT-PCR). Monitoring of specific circRNAs using this SERS-based biosensor is a promising method for cancer diagnosis and gene therapy.

A spectral bias-error stepwise correction method of plasma image-spectrum fusion based on deep learning for improving the performance of LIBS

Poor spectral stability seriously hinders the wide application of laser-induced breakdown spectroscopy (LIBS), so how to improve its stability is the focus, hotspot, and difficulty of current research. In this study, to achieve high precision quantitative analysis under complex detection conditions, utilizing the fusion of multi-dimensional plasma information and the integration of physical models and algorithmic models, a spectral bias-error stepwise correction method of plasma image-spectrum fusion based on deep learning (SBESC-PISF) was proposed. In this method, based on the statistical properties of LIBS spectra, the actual obtained spectra were decomposed into three parts: the ideal spectral intensity related only to the element concentration, and the spectral bias and spectral error caused by the fluctuation of complex high-dimensional plasma parameters. Further, the deep learning methods were used to fully excavate all the effective features in the plasma images and spectra to invert the complex high-dimensional plasma parameters according to the physical models. Finally, the estimation models of spectral bias and spectral error were established based on these features, to realize the high-precision correction of spectral intensity. To verify the feasibility of SBESC-PISF, the spectra of aluminum alloy samples obtained under three complex detection conditions were used for analysis. Under the experimental condition of laser energy fluctuation, after correction by SBESC-PISF, R2 of the three calibration curves was all increased to 0.999, RMSE and STD of the validation set (RMSEV, STDV) were reduced by 55.246 % and 50.167 %, respectively. Under the experimental condition of defocusing amount fluctuation, R2 was also all increased to 0.999, RMSEV and STDV were decreased by 58.201 % and 51.006 %, respectively. When the laser energy and defocusing amount fluctuate simultaneously, R2 was increased to 0.999, 0.996 and 0.988, RMSEV and STDV were reduced by 58.776 % and 54.397 %, respectively. These experimental results demonstrate that the spectral fluctuation correction of SBESC-PISF under complex detection conditions is effective and has wide applicability.

Self-powered multifunctional platform based on dual-photoelectrode for dual-mode detection and inactivation of Salmonella enteritidis

Self-powered photoelectrochemical (PEC) sensing is a novel sensing modality. The introduction of dual-mode sensing and photoelectrocatalysis in a self-powered system enables both detection and sterilization purposes. To this end, herein, a self-powered multifunctional platform for the photoelectrochemical-fluorescence (PEC-FL) detection and in-situ inactivation of Salmonella enteritidis (SE) was constructed. The platform utilized Bi4NbO8Cl/V2CTx/FTO as a photoanode and CuInS2/FTO as a photocathode and incubated quantum dot (QDs) signaling probes on the surface of the photocathode. During detection, the system drives the transfer of photogenerated electrons between the dual photoelectrodes through the Fermi energy level difference. The photoanode amplifies the photoelectric signal, while the photocathode is solely dedicated to the immune recognition process. QDs provide an additional fluorescence signal to the system. Under optimal experimental conditions, the multifunctional platform achieves detection limits of 3.2 and 5.3 CFU/mL in PEC and FL modes respectively, with a detection range of 2.91 × 102 to 2.91 × 108 CFU/mL. With the application of an external bias voltage, it further promotes electron transfer between the dual photoelectrodes, inhibits the recombination of photogenerated electrons and holes. It generates a significant amount of superoxide radicals (·O2-) in the cathodic region, resulting in strong sterilization efficiency (99%). The constructed self-powered multifunctional platform exhibits high sensitivity and sterilization efficiency, it provides a feasible and effective strategy to enhance the comprehensive capability of self-powered sensors.

Precise Methylation Detection of Tumor Suppressor Gene Promoters by Magnetic Enrichment and Nano Silver Adduct-Promoted Surface-Enhanced Raman Scattering

Noninvasive liquid biopsies can be used for early tumor diagnosis by identifying the methylation level of the tumor suppressor genes (TSGs)-a reliable index for cancer evaluation. However, identifying trace circulating genes from specimens remains challenging. This work introduces a novel method that combines magnetic isolation and surface-enhanced Raman scattering (SERS) to concentrate and detect the methylated TSG promotors. A superparamagnetic iron oxide nanoparticle modified with streptavidin is prepared as a universal magnetic bead. Biotin-terminated probe single-strand DNA (ssDNA) is immobilized on the magnetic beads through biotin-streptavidin bioconjugation. Artificial target ssDNA fragments with various methylation levels are applied as a promoter gene model. Concentrated double-strand DNA (dsDNA) is produced by a hybridizing probe and target ssDNA on magnetic nanobeads, as well as an additional magnetic isolation process. The well-prepared DNA adduct, which consists of 3 nm cisplatin-modified Ag nanoclusters, can specifically bind with guanine-cytosine base pairs of dsDNA. Ag-nanoparticle-induced localized SERS amplified signals of 5-methylcytosine (5-mC) from the dsDNA in Raman spectra, enabling accurate methylation level measurement in mixtures of 0-1 µm methylated DNA, with a detection limit of 0.05 µm. This method shows promise for enabling the methylation level evaluation of various TSGs and promoters in early cancer liquid biopsies.

Tailoring metal oxide nanozymes for biomedical applications: trends, limitations, and perceptions

Nanomaterials with enzyme-like properties are known as 'nanozymes'. Nanozymes are preferred over natural enzymes due to their nanoscale characteristics and ease of tailoring of their physicochemical properties such as size, structure, composition, surface chemistry, crystal planes, oxygen vacancy, and surface valence state. Interestingly, nanozymes can be precisely controlled to improve their catalytic ability, stability, and specificity which is unattainable by natural enzymes. Therefore, tailor-made nanozymes are being favored over natural enzymes for a range of potential applications and better prospects. In this context, metal oxide nanoparticles with nanozyme-mimicking characteristics are exclusively being used in biomedical sectors and opening new avenues for future nanomedicine. Realising the importance of this emerging area, here, we discuss the mechanistic actions of metal oxide nanozymes along with their key characteristics which affect their enzymatic actions. Further, in this critical review, the recent progress towards the development of point-of-care (POC) diagnostic devices, cancer therapy, drug delivery, advanced antimicrobials/antibiofilm, dental caries, neurodegenerative diseases, and wound healing potential of metal oxide nanozymes is deliberated. The advantages of employing metal oxide nanozymes, their potential limitations in terms of nanotoxicity, and possible prospects for biomedical applications are also discussed with future recommendations.

Uniform PtCoRuRhFe high-entropy alloy nanoflowers: Multi-site synergistic signal amplification for colorimetric assay of captopril

Uniform PtCoRuRhFe high-entropy alloy nanoflowers (HEANFs) were fabricated by a simple wet-chemical co-reduction method in oleylamine for quantitative colorimetric determination of captopril (CAP) based on multi-site synergistic signal amplification. Specifically, the peroxidase mimetic activity of the PtCoRuRhFe HEANFs was examined through catalysis of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation, whose catalytic mechanism was investigated by electron paramagnetic resonance (EPR) spectroscopy. The role of the ·O2- was figured out during the catalytic procedure. Further, the oxidation of TMB (oxTMB) can be effectively reduced by CAP, accompanied by quickly transforming the solution color from blue to colorless. More importantly, the absorbance at 652 nm is linearly related to the CAP concentration in a range 5.0-50.0 mM with a low detection limit of 2.82 mM. The method has been applied to the determination of CAP in human urine samples. It offers a simple and high-efficiency method for facile and visual detection of CAP in hospitals.

A colorimetric platform using highly active Prussian blue composite nanocubes for the rapid determination of ascorbic acid and acid phosphatase

Cobalt-doped Prussian blue composite nanocubes (Co-PB NCs) were synthesized, which can quickly convert O2 to O2•- and 1O2. Due to the presence of cobalt and iron transition metal redox electron pairs, Co-PB NCs with high oxidase mimetic activity can rapidly oxidize the substrate 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue products (ox-TMB) without the assistance of unstable H2O2. Using ascorbic acid-2-phosphate trisodium salt (AAP) as a substrate, it can be converted to reduced ascorbic acid (AA) under acid phosphatase (ACP) hydrolysis, resulting in suppression of TMB oxidation. Therefore, an enzyme cascade signal amplification strategy for rapid colorimetric detection of AA/ACP was developed based on the high-efficiency oxidase-like activity of Co-PB NCs combined with the hydrolysis effect of ACP. The color changes at low concentrations of AA and ACP could be observed by the naked eye, and the detection limits of AA and ACP were 1.67 μM and 0.0266 U/L, respectively. The developed colorimetric method was applied to the determination of AA in beverages and ACP in human serum, and the RSDs were less than 3%, showing good reproducibility. This work provides a promising strategy for the use of metal-doped Prussian blue composite material for the construction of rapid colorimetric sensing platforms that avoid the use of unstable hydrogen peroxide.

Synergistic signal-amplification effect of silver nanowires and bifunctional monomers on molecularly imprinted electrochemical sensor for diuron analysis

Molecularly imprinted polymers (MIP) have been widely owing to their specificity, however, their singular structure imposes limitations on their performance. Current enhancement methods, such as doping with inorganic nanomaterials or introducing various functional monomers, are limited and single, indicating that MIP performances require further advancement. In this work, a dual-modification approach that integrates both conductive inorganic nanomaterials and diverse bifunctional monomers was proposed to develop a multifunctional MIP-based electrochemical (MMIP-EC) sensor for diuron (DU) detection. The MMIP was synthesized through a one-step electrochemical copolymerization of silver nanowires (AgNWs), o-phenylenediamine (O-PD), and 3,4-ethylenedioxythiophene (EDOT). DU molecules could conduct fluent electron transfer within the MMIP layer through the interaction between anchored AgNWs and bifunctional monomers, and the abundant recognition sites and complementary cavity shapes ensured that the imprinted cavities exhibit high specificity. The current intensity amplified by the two modification strategies of MMIP (3.7 times) was significantly higher than the sum of their individual values (3.2 times), exerting a synergistic effect. Furthermore, the adsorption performance of the MMIP was characterized by examining the kinetics and isotherms of the adsorption process. Under optimal conditions, the MMIP-EC sensor exhibits a wide linear range (0.2 ng/mL to 10 μg/mL) for DU detection, with a low detection limit of 89 pg/mL and excellent selectivity (an imprinted factor of 10.4). In summary, the present study affords innovative perspectives for the fabrication of MIP-EC sensor with superior analytical performance.

Reusable fluorescence nanoprobe based on DNA-functionalized metal-organic framework for ratiometric detection of mercury (II) ions

A reusable fluorescent nanoprobe was developed using DNA-functionalized metal-organic framework (MOF) for ratiometric detection of Hg2+. We utilized a zirconium-based MOF (UiO-66) to encapsulate tris(bipyridine) ruthenium(II) chloride (Ru(bpy)32+), resulting in Ru(bpy)32+@UiO-66 (RU) with red fluorescence. The unsaturated metal sites in UiO-66 facilitate the attachment of thymine-rich single-strand DNA (T-ssDNA) through Zr-O-P bond, producing T-ssDNA-functionalized RU complex (RUT). The T-ssDNA selectively binds to Hg2+, forming stable T-Hg2+-T base pairs and folding into double-stranded DNA, which permits the intercalation of SYBR Green I (SGI) and activates its green fluorescence. In the presence of Hg2+, SGI fluorescence increases in a dose-dependent manner, while Ru(bpy)32+ fluorescence remains constant. This fluorescence contrast enables RUT to serve as an effective ratiometric nanoprobe for Hg2+ detection, with a detection limit of 3.37 nM. Additionally, RUT demonstrates exceptional reusability due to the ability of cysteine to remove Hg2+, given its stronger affinity for thiol groups. The RUT was successfully applied to detect Hg2+ in real water samples. This work advances the development of ratiometric fluorescence nanoprobe based on DNA-functionalized MOFs.

Application of Nanozymes and its Progress in the Treatment of Ischemic Stroke

Nanozymes are a new kind of material which has been applied since the beginning of this century, and its birth has promoted the development of chemistry, materials science, and biology. Nanozymes can be used as a substitute for natural enzyme and has a wide range of applications; therefore, it has attracted extensive attention from all sectors of the community, and the number of studies has constantly increasing. In this paper, we introduced the outstanding achievements in the field of nanozymes in recent years from the main function, the construction of nanozyme-based biosensors, and the treatment of ischemic stroke, and we also illustrated the internal mechanism and the catalytic principle. In the end, the obstacles and challenges in the future development of nanozymes were proposed.

Hollow-like three-dimensional structure of methyl orange-delaminated Ti3C2 MXene nanocomposite for high-performance electrochemical sensing of tryptophan

Tryptophan(Trp) is being explored as a potential biomarker for various diseases associated with decreased tryptophan levels; however, metabolomic methods are expensive and time-consuming and require extensive sample analysis, making them urgently needed for trace detection. To exploit the properties of Ti3C2 MXenes a rational porous methyl orange (MO)-delaminated Ti3C2 MXene was prepared via a facile mixing process for the electrocatalytic oxidation of Trp. The hollow-like 3D structure with a more open structure and the synergistic effect of MO and conductive Ti3C2 MXene enhanced its electrochemical catalytic capability toward Trp biosensing. More importantly, MO can stabilize Ti3C2 MXene nanosheets through noncovalent π-π interactions and hydrogen bonding. Compared with covalent attachment, these non-covalent interactions preserve the electronic conductivity of the Ti3C2 MXene nanosheets. Finally, the addition of MO-derived nitrogen (N) and sulfur (S) atoms to Ti3C2 MXene enhanced the electronegativity and improved its affinity for specific molecules, resulting in high-performance electrocatalytic activity. The proposed biosensor exhibited a wide linear response in concentration ranges of 0.01-0.3 µM and 0.5-120 µM, with a low detection limit of 15 nM for tryptophan detection, and high anti-interference ability in complex media of human urine and egg white matrices. The exceptional abilities of the MO/Ti3C2 nanocatalyst make it a promising electrode material for the detection of important biomolecules.

Magnetic self-assembled label-free electrochemical biosensor based on Fe3O4/α-Fe2O3 heterogeneous nanosheets for the detection of Tau proteins

A type of electrochemical biosensors based on magnetic Fe3O4/α-Fe2O3 heterogeneous nanosheets was constructed to detect Tau proteins for early diagnosis and intervention therapy of Alzheimer's disease (AD). Firstly, Fe3O4/α-Fe2O3 heterogeneous nanosheets were fabricated as the substrate to realize magnetic self-assembly and magnetic separation to improve current response, and Fe3O4/α-Fe2O3@Au-Apt/ssDNA/MCH biosensors were successfully constructed through the reduction process of chloroauric acid, the immobilizations of aptamer (Apt) and ssDNA, and the intercept process of 6-Mercapto-1-hexanol (MCH); the construction process of the electrochemical biosensor was monitored using Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the factors affecting the current response of this sensor (concentration of Fe3O4/α-Fe2O3@Au and Apt/ssDNA, incubation temperature and time of Tau) were explored and optimized using differential pulse voltammetry (DPV). Analyzing the performance of this sensor under optimal conditions, the linear range was finally obtained to be 0.1 pg/mL-10 ng/mL, the limit of detection (LOD) was 0.08 pg/mL, and the limit of quantification (LOQ) was 0.28 pg/mL. The selectivity, reproducibility and stability of the biosensors were further investigated, and in a really sample analysis using human serum, the recoveries were obtained in the range of 93.93 %-107.39 %, with RSD ranging from 1.05 % to 1.94 %.

Electrochemical DNA-nano biosensor for the detection of Goserelin as anticancer drug using modified pencil graphite electrode

Goserelin is an effective anticancer drug, but naturally causes several side effects. Hence the determination of this drug in biological samples, plays a key role in evaluating its effects and side effects. The current studies have concentrated on monitoring Goserelin using an easy and quick DNA biosensor for the first time. In this study, copper(II) oxide nanoparticles were created upon the surface of multiwalled carbon nanotubes (CuO/MWCNTs) as a conducting mediator. The modified pencil graphite electrode (ds-DNA/PA/CuO/MWCNTs/PGE) has been modified with the help of polyaniline (PA), ds-DNA, and CuO/MWCNTs nanocomposite. Additionally, the issue with the bio-electroanalytical guanine oxidation signal in relation to ds-DNA at the surface of PA/CuO/MWCNTs/PGE has been examined to determination Goserelin for the first time. It also, established a strong conductive condition to determination Goserelin in nanomolar concentration. Thus, Goserelin's determining, however, has a 0.21 nM detection limit and a 1.0 nM-110.0 µM linear dynamic range according to differential pulse voltammograms (DPV) of ds-DNA/PA/CuO/MWCNTs/PGE. Furthermore, the molecular docking investigation highlighted that Goserelin is able to bind ds-DNA preferentially and supported the findings of the experiments. The determining of Goserelin in real samples has been effectively accomplished in the last phase using ds-DNA/PA/CuO/MWCNTs/PGE.

Label-free fluorescence detection of human 8-oxoguanine DNA glycosylase activity amplified by target-induced rolling circle amplification

BACKGROUND

Human 8-oxoG DNA glycosylase 1 (hOGG1) is one of the important members of DNA glycosylase for Base excision repair (BER), the abnormal activity of which can lead to the failure of BER and the appearance of various diseases, such as breast cancer, bladder cancer, Parkinson's disease and lung cancer. Therefore, it is important to detect the activity of hOGG1. However, traditional detection methods suffer from time consuming, complicated operation, high false positive results and low sensitivity. Thus, it remains a challenge to develop simple and sensitive hOGG1 analysis strategies to facilitate early diagnosis and treatment of the relative disease.

RESULTS

A target-induced rolling circle amplification (TIRCA) strategy for label-free fluorescence detection of hOGG1 activity was proposed with high sensitivity and specificity. The TIRCA strategy was constructed by a hairpin probe (HP) containing 8-oxoG site and a primer probe (PP). In the presence of hOGG1, the HP transformed into dumbbell DNA probe (DDP) after the 8-oxoG site of which was removed. Then the DDP formed closed circular dumbbell probe (CCDP) by ligase. CCDP could be used as amplification template of RCA to trigger RCA. The RCA products containing repeated G4 sequences could combine with ThT to produce enhanced fluorescence, achieving label-free fluorescence sensing of hOGG1. Given the high amplification efficiency of RCA and the high fluorescence quantum yield of the G4/ThT, the proposed TIRCA achieved highly sensitive measurement of hOGG1 activity with a detection limit of 0.00143 U/mL. The TIRCA strategy also exhibited excellent specificity for hOGG1 analysis over other interference enzymes.

SIGNIFICANCE

This novel TIRCA strategy demonstrates high sensitivity and high specificity for the detection of hOGG1, which has also been successfully used for the screening of inhibitors and the analysis of hOGG1 in real samples. We believe that this TIRCA strategy provides new insight into the use of the isothermal nucleic acid amplification as a useful tool for hOGG1 detection and will play an important role in disease early diagnosis and treatment.

Application of the Peroxidase‒like Activity of Nanomaterials for the Detection of Pathogenic Bacteria and Viruses

Infectious diseases caused by pathogenic bacteria and viruses pose a significant threat to human life and well-being. The prompt identification of these pathogens, characterized by speed, accuracy, and efficiency, not only aids in the timely screening of infected individuals and the prevention of further transmission, but also facilitates the precise diagnosis and treatment of patients. Direct smear microscopy, microbial culture, nucleic acid-based polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA) based on microbial surface antigens or human serum antibodies, have made substantial contributions to the prevention and management of infectious diseases. Due to its shorter processing time, simple equipment requirements, and no need for professional and technical personnel, ELISA has inherent advantages over other methods for detecting pathogenic bacteria and viruses. Horseradish peroxidase mediated catalysis of substrate coloration is the key for the detection of target substances in ELISA. However, the variability, high cost, and environmental susceptibility of natural peroxidase greatly limit the application of ELISA in pathogen detection. Compared with natural enzymes, nanomaterials with enzyme-mimicking activity are inexpensive, highly environmentally stable, easy to store and mass producing, etc. Based on their peroxidase-like activities and unique physicochemical properties, nanomaterials can greatly improve the efficiency and ease of use of ELISA-like detection methods for pathogenic bacteria and viruses. This review introduces recent advances in the application of nanomaterials with peroxidase-like activity for the detection of pathogenic bacteria (both gram-negative bacteria and gram-positive bacteria) and viruses (both RNA viruses and DNA viruses). The emphasis is on the detection principle and the evaluation of effectiveness. The limitations and prospects for future translations are also discussed.

A Rapid and Sensitive Gold Nanoparticle-Based Lateral Flow Immunoassay for Chlorantraniliprole in Agricultural and Environmental Samples

Chlorantraniliprole (CAP) is a new type of diamide insecticide that is mainly used to control lepidopteran pests. However, it has been proven to be hazardous to nontarget organisms, and the effects of its residues need to be monitored. In this study, five hybridoma cell lines were developed that produced anti-CAP monoclonal antibodies (mAbs), of which the mAb originating from the cell line 5C5B9 showed the highest sensitivity and was used to develop a gold nanoparticle-based lateral flow immunoassay (AuNP-LFIA) for CAP. The visible limit of detection of the AuNP-LFIA was 1.25 ng/mL, and the detection results were obtained in less than 10 min. The AuNP-LFIA showed no cross-reactivity for CAP analogs, except for tetraniliprole (50%) and cyclaniliprole (5%). In the detection of spiked and blind samples, the accuracy and reliability of the AuNP-LFIA were confirmed by a comparison with spiked concentrations and verified by ultra-performance liquid chromatography-tandem mass spectrometry. Thus, this study provides the core reagents for establishing CAP immunoassays and a AuNP-LFIA for the detection of residual CAP.

Advances of Electrochemical and Electrochemiluminescent Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs), a rapidly developing category of crystalline conjugated organic polymers, possess highly ordered structures, large specific surface areas, stable chemical properties, and tunable pore microenvironments. Since the first report of boroxine/boronate ester-linked COFs in 2005, COFs have rapidly gained popularity, showing important application prospects in various fields, such as sensing, catalysis, separation, and energy storage. Among them, COFs-based electrochemical (EC) sensors with upgraded analytical performance are arousing extensive interest. In this review, therefore, we summarize the basic properties and the general synthesis methods of COFs used in the field of electroanalytical chemistry, with special emphasis on their usages in the fabrication of chemical sensors, ions sensors, immunosensors, and aptasensors. Notably, the emerged COFs in the electrochemiluminescence (ECL) realm are thoroughly covered along with their preliminary applications. Additionally, final conclusions on state-of-the-art COFs are provided in terms of EC and ECL sensors, as well as challenges and prospects for extending and improving the research and applications of COFs in electroanalytical chemistry.

Direct, ultrafast, and sensitive detection of environmental pathogenic microorganisms based on a graphene biosensor

Pathogenic microorganisms in the environment pose a serious threat to global human health. This study developed a reduced graphene oxide (rGO)-field effect transistor (FET) biosensor to realize the rapid and sensitive detection of pathogenic microorganisms. The rGO-FET sensors were prepared by in-situ thermal reduction method, and biorecognition elements were immobilized using a crosslinking agent to realize the surface functionalization of rGO. The rGO-FET biosensors can detect Escherichia coli O157:H7 as low as 1.4 CFU mL-1 within 46 s. The normalized current response was linearly correlated with E. coli concentration in the range of 1.4-1.4 × 107 CFU mL-1. The normalized current response of E. coli O157:H7 was about an order of magnitude higher than those of other microorganisms, indicating that the biosensor has good specificity. The current loss rates of the unmodified rGO-FET sensors and the biosensors modified with anti-E. coli O157:H7 after 30 days of storage at 4 °C were approximately 8% and 15%, respectively. Most importantly, the rGO-FET biosensors can directly detect real samples without pretreatment. Compared with other technologies, the rGO-FET biosensors can detect pathogenic microorganisms with a wider linear range in a shorter time, which is of great importance for the rapid warning and control of pathogenic microorganisms in the environment.

Paper-based colorimetric sensors for point-of-care testing

By eliminating the need for sample transportation and centralized laboratory analysis, point-of-care testing (POCT) enables on-the-spot testing, with results available within minutes, leading to improved patient management and overall healthcare efficiency. Motivated by the rapid development of POCT, paper-based colorimetric sensing, a powerful analytical technique that exploits the changes in color or absorbance of a chemical species to detect and quantify analytes of interest, has garnered increasing attention. In this review, we strive to provide a bird's eye view of the development landscape of paper-based colorimetric sensors that harness the unique properties of paper to create low-cost, easy-to-use, and disposable analytical devices, thematically covering both fundamental aspects and categorized applications. In the end, we authors summarized the review with the remaining challenges and emerging opportunities. Hopefully, this review will ignite new research endeavors in the realm of paper-based colorimetric sensors.

A sensitive and rapid electrochemical biosensor for sEV-miRNA detection based on domino-type localized catalytic hairpin assembly

Small extracellular-vesicule-associated microRNA (sEV-miRNA) is an important biomarker for cancer diagnosis. However, rapid and sensitive detection of low-abundance sEV-miRNA in clinical samples is challenging. Herein, a simple electrochemical biosensor that uses a DNA nanowire to localize catalytic hairpin assembly (CHA), also called domino-type localized catalytic hairpin assembly (DT-LCHA), has been proposed for sEV-miRNA1246 detection. The DT-LCHA offers triple amplification, (i). CHA system was localized in DNA nanowire, which shorten the distance between hairpin substrate, inducing the high collision efficiency of H1 and H2 and domino effect. Then, larger numbers of CHAs were triggered, capture probe bind DT-LCHA by exposed c sites. (ii) The DNA nanowire can load large number of electroactive substance RuHex as amplified electrochemical signal tags. (iii) multiple DT-LCHA was carried by the DNA nanowire, only one CHA was triggered, the DNA nanowire was trapped by the capture probe, which greatly improve the detection sensitivity, especially when the target concentration is extremely low. Owing to the triple signal amplification in this strategy, sEV-miRNA at a concentration of as low as 24.55 aM can be detected in 20 min with good specificity. The accuracy of the measurements was also confirmed using reverse transcription quantitative polymerase chain reaction. Furthermore, the platform showed good performance in discriminating healthy donors from patients with early gastric cancer (area under the curve [AUC]: 0.96) and was equally able to discriminate between benign gastric tumors and early cancers (AUC: 0.77). Thus, the platform has substantial potential in biosensing and clinical diagnosis.

Dual-mode colorimetric and homogeneous electrochemical detection of intracellular/extracellular H2O2 based on FeSx/SiO2 nanoparticles with high peroxidase-like activity

Abnormal expression of hydrogen peroxide (H₂O₂) elucidates cell dysfunctions and might induce the occurrence and deterioration of various diseases. However, limited by its ultralow level under pathophysiological conditions, intracellular and extracellular H₂O₂ was difficult to be detected accurately. Herein, a colorimetric and homogeneous electrochemical dual-mode biosensing platform was constructed for intracellular/extracellular H₂O₂ detection based on FeS_x/SiO₂ nanoparticles (FeS_x/SiO₂ NPs) with high peroxidase-like activity. In this design, FeS_x/SiO₂ NPs were synthesized with excellent catalytic activity and stability compared to natural enzymes, which improved the sensitivity and stability of sensing strategy. 3,3',5,5'-Tetramethylbenzidine (TMB), as a multifunctional indicator, was oxidized in the presence of H₂O₂, generated color changes and realized visual analysis. In this process, the characteristic peak current of TMB decreased, which could realize the ultrasensitive detection of H₂O₂ by homogeneous electrochemistry. Accordingly, by integrating visual analysis ability of colorimetry and the high sensitivity of homogeneous electrochemistry, the dual-mode biosensing platform exhibited high accuracy, sensitivity and reliability. The detection limits of H₂O₂ were 0.2 μM (S/N = 3) for the colorimetric method and 2.5 nM (S/N = 3) for the homogeneous electrochemistry assay. Therefore, the dual-mode biosensing platform provided a new opportunity for highly accurate and sensitive detection of intracellular/extracellular H₂O₂.