Covalent Organic Framework-Structured Raman Probes for Ultrasensitive In Vivo Bioimaging.

Organic Raman probes, including polymers and small molecules, have attracted great attention in biomedical imaging owing to their excellent biocompatibility. However, the development of organic Raman probes is usually hindered by a mismatch between their absorption spectra and wavelength-fixed excitation, which makes it difficult to achieve resonance excitation necessary to obtain strong Raman signals. Herein, we introduce a covalent organic framework (COF) into the fine absorption spectrum regulation of organic Raman probes, resulting in their significant Raman signal enhancement. In representative examples, a polymer poly(diketopyrrolopyrrole-p-phenylenediamine) (DPP-PD) and a small molecule azobenzene are transformed into the corresponding COF-structured Raman probes. Their absorption peaks show an accurate match of less than 5 nm with the NIR excitation. As such, the COF-structured Raman probes acquire highly sensitive bioimaging capabilities compared to their precursors with negligible signals. By further mechanism studies, we discover that the crystallinity and size of COFs directly affect the π-conjugation degree of Raman probes, thus changing their bandgaps and absorption spectra. Our study offers a universal and flexible method for improving the signal performance of organic Raman probes without changing their structural units, making it more convenient to obtain the highly sensitive organic Raman probes for in vivo bioimaging.

Visual Sensor Array for Multiple Aromatic Amines via Specific Ascorbic Acid Oxidase Mimic Triggered Schiff-Base Chemistry.

Redox nanozymes have exhibited various applications in recognizing environmental pollutants but not aromatic amines (a type of typical pollutant). Herein, with Cu2+ as a node and tryptophan (Trp) as a linker, Cu-Trp as a specific ascorbic acid oxidase mimic was synthesized, which could catalyze ascorbic acid (AA) oxidation to dehydroascorbic acid (DHAA). Alternatively, with other natural amino acids as linkers to synthesize Cu-based nanozymes, such catalytic performances are also observed. The as-produced DHAA could react with o-phenylenediamine (OPD) and its derivatives (2,3-naphthalene diamine (NDA), 4-nitro-o-phenylenediamine (4-NO2-OPD), 4-fluoro-o-phenylenediamine (4-F-OPD), 4-chloro-o-phenylenediamine(4-Cl-OPD), and 4-bromo-o-phenylenediamine(4-Br-OPD)) to form a Schiff base and emit fluorescence. Based on the results, with Cu-Trp + AA and Cu-Arg (with arginine (Arg) as a linker) + AA as two sensing channels and extracted red, green, and blue (RGB) values from emitted fluorescence as read-out signals, a visual sensor array was constructed to efficiently distinguish OPD, NDA, 4-NO2-OPD, 4-F-OPD, 4-Cl-OPD, and 4-Br-OPD as low as 10 µM. Such detecting performance was further confirmed through discriminating binary, ternary, quinary, and senary mixtures with various concentration ratios, recognizing 18 unknown samples, and even quantitatively analyzing single aromatic amine. Finally, the discriminating ability was further validated in environmental waters, providing an efficient assay for large-scale scanning levels of multiple aromatic amines.

Bioinspired Heterocoordination in Adaptable Cobalt Metal-Organic Framework for DNA Epigenetic Modification Detection.

Metal-organic frameworks (MOFs) show unique advantages in simulating the dynamics and fidelity of natural coordination. Inspired by zinc finger protein, a second linker was introduced to affect the homogeneous MOF system and thus facilitate the emergence of diverse functionalities. Under the systematic identification of 12 MOF species (i.e., metal ions, linkers) and 6 second linkers (trigger), a dissipative system consisting of Co-BDC-NO2 and o-phenylenediamine (oPD) was screened out, which can rapidly and in situ generate a high photothermal complex (η = 36.9%). Meanwhile, both the carboxylation of epigenetic modifications and metal ion (Fe3+, Ni2+, Cu2+, Zn2+, Co2+ and Mn2+) screening were utilized to improve the local coordination environment so that the adaptable Co-MOF growth on the DNA strand was realized. Thus, epigenetic modification information on DNA was converted to an amplified metal ion signal, and then oPD was further introduced to generate bimodal dissipative signals by which a simple, high-sensitivity detection strategy of 5-hydroxymethylcytosine (LOD = 0.02%) and 5-formylcytosine (LOD = 0.025‰) was developed. The strategy provides one low-cost method (< 0.01 $/sample) for quantifying global epigenetic modifications, which greatly promotes epigenetic modification-based early disease diagnosis. This work also proposes a general heterocoordination design concept for molecular recognition and signal transduction, opening a new MOF-based sensing paradigm.

An electrochemical sensor based on molecularly imprinted poly(o-phenylenediamine) for the detection of thymol.

A molecularly imprinted electrochemical sensor was facilely fabricated for the detection of thymol (THY). o-Phenylenediamine (oPD) was used as the functional monomer and electropolymerized on the surface of the glassy carbon electrode (GCE) by using THY as the templates. After the THY templates were removed with 50 % (v/v) ethanol, imprinted cavities complementary to the templates were formed within the poly(o-phenylenediamine) (PoPD) films. The resultant molecularly imprinted PoPD/GCE (MI-PoPD/GCE) was used for the detection of THY, and a wide linear range from 0.5 to 100 µM with a low limit of detection (LOD) of 0.084 µM were obtained under the optimal conditions. The developed MI-PoPD/GCE also displays high selectivity, reproducibility and stability for THY detection. Finally, the content of THY in the real samples was accurately determined by the as-fabricated MI-PoPD/GCE, demonstrating its high practicability and reliability.

The Interaction of Myeloperoxidase with the Industrial Contaminant 6-PPD: A Potential Pathway for Reactive Metabolites.

6-PPD (N-[1,3-dimethylbutyl]-N'-phenyl-p-phenylenediamine) is an industrial antioxidant reported to be an environmental contaminant. It was found to be highly toxic to coho salmon and potentially other aquatic organisms. The toxicity of 6-PPD in humans, however, remains unknown. The neutrophil enzyme myeloperoxidase (MPO) is known to catalyze xenobiotic metabolism; therefore, its role in 6-PPD cytotoxicity was investigated using the MPO-rich HL-60 cell line. UV-visible spectroscopy and liquid chromatography-mass spectrometry (LC/MS) were performed to investigate the MPO-mediated oxidation of 6-PPD and identify possible metabolites in the absence and presence of glutathione (GSH). 6-PPD's cytotoxicity, effect on mitochondrial membrane potential (MMP), and GSH-depleting ability in HL-60 cells were assessed. Electron paramagnetic resonance (EPR) was used to determine GSH radical formation using DMPO, and mitochondrial-derived superoxide was assessed with the mito-TEMPO-H probe. Evaluation of the 6-PPD-induced cellular injury pathways was performed by preincubating an antioxidant and an MPO inhibitor with HL-60 cells. UV-vis analysis of MPO-catalyzed oxidation of 6-PPD demonstrated changes in the 6-PPD spectrum, whereas the addition of GSH altered the spectrum, indicating possible GSH conjugate formation. LC/MS showed the formation of multiple products, including GSH-6-PPD conjugates and a GSH conjugate to a 4-hydroxydiphenylamine (a known 6-PPD degradant), which could potentially induce cytotoxicity. 6-PPD demonstrated concentration-dependent cytotoxicity, and cellular GSH levels were decreased by 6-PPD. Similarly, the level of MMP decreased, suggesting mitochondrial depolarization. Furthermore, the EPR spin probe for mitochondrial superoxide showed a positive relationship with 6-PPD concentration, and EPR spin-trapping demonstrated 6-PPD concentration-dependent GSH radical signal intensity using MPO/H2O2. The GSH precursor, NAC, demonstrated partial cytoprotection against 6-PPD; however, the MPO inhibitor PF-1355 surprisingly showed no significant cytoprotective effect. Our results suggest that MPO could be a potential catalyst for 6-PPD toxicity in humans. However, MPO inhibition did not significantly affect cellular viability, suggesting an MPO-independent toxicity pathway. These findings warrant a deeper investigation to determine 6-PPD mammalian toxicity pathways.

Dual-Level Reactive Oxygen Species Amplifier for Enhanced Photothermal-Chemodynamic Therapy.

Chemodynamic therapy is an appealing modality in cancer treatment. However, its therapeutic effectiveness is impeded by insufficient catalytic efficiency and overexpression of glutathione (GSH) at the tumor site. In this study, a poly(o-phenylenediamine) (PoPD)@copper sulfide (CuS) nanoplatform was developed as dual-level reactive oxygen species (ROS) amplifier for enhanced photothermal-chemodynamic therapy. The PoPD@CuS nanoplatform exhibited photothermal performance, chemodynamic performance, and GSH-depleting capability. Alongside its improved photothermal conversion efficiency with tumor pH-responsiveness, the photothermal behavior of PoPD@CuS could elevate chemodynamic activity by regulating the temperature spatiotemporally, leading to increased ROS production. Moreover, GSH depletion of PoPD@CuS could suppress ROS scavenging, further enhancing oxidative stress in the tumor region. Consequently, functioning as a dual-level ROS amplifier, PoPD@CuS showcased remarkable effectiveness in photothermal-chemodynamic combination therapy.

Engineering fluorescent NO probes for live-monitoring cellular inflammation and apoptosis.

The processes of apoptosis and inflammatory responses, which are defensive strategies used by cells to confront external substances, can give rise to diverse diseases when prolonged or disrupted, such as cancer, Alzheimer's disease, and Parkinson's disease. Here we engineered a live-cell imaging fluorescent probe for nitric oxide (NO) based on naphthalimide and o-phenylenediamine, enabling the sensitive detection of NO in cancer cells and thereby live-monitoring of the doxorubicin-induced apoptosis and lipopolysaccharide-triggered inflammation reactions. Importantly, we found that the level of released NO can sensitively indicate the early stages of both cellular inflammatory responses and apoptotic processes. This suggested that cellular NO in fact behaves as a new class of signaling molecule for inflammatory responses and apoptosis processes, providing a potent tool for live-monitoring cellular physiological reactions.

Dual-mode colorimetric and fluorescence detection of BRCA1 based on a CRISPR-Cas12a system.

Breast cancer, the most common malignant tumor in the world, seriously threatens human life and health. Early diagnosis of breast cancer may help enhance the survival rate. In this work, a colorimetric and fluorescent dual-mode biosensor based on the CRISPR-Cas12a system was constructed to detect the breast cancer biomarker BRCA1. The intact G4 DNA, with the assistance of K+ and hemin, catalyses the oxidation of o-phenylenediamine (OPD) with the assistance of hydrogen peroxide (H2O2), generating the oxidation product 2,3-diaminophenazine (DAP), which has distinct absorption and fluorescence peaks. The presence of the target BRCA1 activates the trans-cleavage activity of CRISPR-Cas12a, leading to the cleavage of G4 DNA and inhibiting the catalytic oxidation of OPD. Target BRCA1 was quantitatively determined by measuring both the absorbance and fluorescence intensity of DAP. The detection limits were calculated to be 0.615 nM for the colorimetric method and 0.289 nM for the fluorescence method. The dual-mode biosensor showed good selectivity and reliability for BRCA1 and can resist interference from complex substrates, and it has great potential in biomedical detection.

A nano-biosensing platform based on CuS-BSA for label-free fluorescence detection of Escherichia coli.

Bacterial contamination is a serious issue for public health and food safety. In this work, a simple and label-free fluorescence detection nanoplatform for Escherichia coli (E. coli) was established on the basis of the competitive relationship for the reduction of Cu2+ in CuS-BSA between E. coli and O-phenylenediamine (OPD). OPD could be directly oxidized by Cu2+ to produce 2,3-diaminophenazine (ox OPD) with fluorescence properties. When OPD was introduced into an aqueous solution containing CuS-BSA and E. coli, the oxidation of OPD was inhibited owing to the reduction of Cu2+ to Cu+/Cu0 by NADH-2 dehydrogenase in the bacterial copper homeostasis mechanism, thus decreasing the fluorescence response signal of the system. Meanwhile, our strategy exhibited a satisfactory performance with a broad linear response to E. coli ranging from 12 to 1.2 × 107 CFU mL-1, and the limit of detection was 9 CFU mL-1. The practicability of the developed fluorescence biosensing platform in real samples was evaluated by successful determination of E. coli in drinking water and orange juice. These findings provide a new sensing strategy for analyzing other foodborne bacteria and ensuring food safety assessment.

Synthesis and biological evaluation of ferrostatin-based diamide derivatives as new ferroptosis inhibitors.

Ferroptosis, a distinct type of cell death caused by iron and lipid peroxidation, has been associated with several diseases, including cardiovascular disorders. Ferrostatin-1 (Fer-1) is a known ferroptosis inhibitor, but its clinical application is limited by low efficacy and stability. In the present study, a series of Fer-1-based diamide derivatives was synthesized and evaluated to enhance ferroptosis inhibition and in vitro metabolic stability. The synthesized compounds were tested for their protective effects against Erastin-induced injury in human vascular endothelial cells (HUVECs). Among the derivatives, compound 36 exhibited the most potent anti-ferroptosis activity with an EC50 value of 0.58 ± 0.02 µM. Remarkably, compound 36 also demonstrated superior stability in both microsomal (human and mouse) and mouse plasma assays. These findings indicated ferroptosis inhibitor 36 as a promising hit for further developing potential therapeutic drug candidates in cardiovascular diseases.

Selectively lighting up glyoxal in living cells using an o-phenylenediamine fused hemicyanine.

Glyoxal (GL) is a reactive α-dicarbonyl compound generated from glycated proteins in the Maillard reaction. It has attracted particular attention over the past few years because of its possible clinical significance in chronic and age-related diseases. In this work, a reaction-based red emission fluorescent probe GL1 has been synthesized successfully by grafting an alkyl group onto an amino group to regulate its selectivity for GL. Under physiological conditions, the fluorescence intensity of GL1 at 640 nm obviously increased with the increase of GL concentration, and it exhibited high selectivity for GL over other reactive carbonyl compounds, as well as a lower detection limit (0.021 µM) and a larger Stokes shift (112 nm). At the same time, GL1 can selectively accumulate in mitochondria and can be used to detect exogenous and endogenous GL in living cells with low cytotoxicity.

Fragmentation Pattern-Based Screening Strategy Combining Diagnostic Ion and Neutral Loss Uncovered Novel para-Phenylenediamine Quinone Contaminants in the Environment.

Identifying transformed emerging contaminants in complex environmental compartments is a challenging but meaningful task. Substituted para-phenylenediamine quinones (PPD-quinones) are emerging contaminants originating from rubber antioxidants and have been proven to be toxic to the aquatic species, especially salmonids. The emergence of multiple PPD-quinones in various environmental matrices and evidence of their specific hazards underscore the need to understand their environmental occurrences. Here, we introduce a fragmentation pattern-based nontargeted screening strategy combining full MS/All ion fragmentation/neutral loss-ddMS2 scans to identify potential unknown PPD-quinones in different environmental matrices. Using diagnostic fragments of m/z 170.0600, 139.0502, and characteristic neutral losses of 199.0633, 138.0429 Da, six known and three novel PPD-quinones were recognized in air particulates, surface soil, and tire tissue. Their specific structures were confirmed, and their environmental concentration and composition profiles were clarified with self-synthesized standards. N-(1-methylheptyl)-N'-phenyl-1,4-benzenediamine quinone (8PPD-Q) and N,N'-di(1,3-dimethylbutyl)-p-phenylenediamine quinone (66PD-Q) were identified and quantified for the first time, with their median concentrations found to be 0.02-0.21 µg·g-1 in tire tissue, 0.40-2.76 pg·m-3 in air particles, and 0.23-1.02 ng·g-1 in surface soil. This work provides new evidence for the presence of unknown PPD-quinones in the environment, showcasing a potential strategy for screening emerging transformed contaminants in the environment.

Design, synthesis, and evaluation of formylpiperazine analogs of Ferrostatin-1 as novel improved ferroptosis inhibitors.

In this study, a series of new formylpiperazine-derived ferroptosis inhibitors were designed and synthesized based on the structure of a known ferroptosis inhibitor, ferrostatin-1 (Fer-1). The anti-ferroptosis activity of these synthetic compounds in human umbilical vein endothelial cells (HUVECs) induced by Erastin was evaluated. It was found that some of the new compounds, especially compound 26, showed potent anti-ferroptosis activity, as evidenced by its ability to restore cell viability, reduce iron accumulation, scavenge reactive oxygen species, maintain mitochondrial membrane potential, increase GSH levels, decrease LPO and MDA content, and upregulate GPX4 expression. Moreover, compound 26 exhibited superior microsomal stability than Fer-1. The present results suggest that compound 26 is a promising lead compound for the development of new ferroptosis inhibitors for the treatment of vascular diseases.

Polyoxometalate-based iron-organic complex nanozymes with peroxidase-like activities for colorimetric detection of hydrogen peroxide and ascorbic acid.

As a new type of artificial enzyme, a nanozyme is an ideal substitute for natural enzymes and has been successfully applied in many fields. However, in the application of biomolecular detection, most nanozymes have the disadvantages of long reaction times or high detection limits, prompting researchers to search for new efficient nanozymes. In this work, the enzyme-like activities of three polyoxometalate-based iron-organic complexes ([Fe(bpp)2](Mo6O19), [Fe(bpp)2]2(Mo8O26)·2CH3OH, and [Fe(bpp)2]4H[Na(Mo8O26)]3), namely, FeMo6, Fe2Mo8, and Fe4Mo8Na, were analyzed. All three polyoxometalate-based iron-organic complexes were found to be capable of catalyzing hydrogen peroxide (H2O2) to oxidize 3,3',5,5'-tetramethylbenzidine and o-phenylenediamine, resulting in visible color changes, further exhibiting peroxidase-like activity. Results showed that Fe4Mo8Na had more active sites due to its long chain structure, endowing more prominent peroxidase-like activity compared with Fe2Mo8 and FeMo6. A colorimetric sensing platform for H2O2 and ascorbic acid detection based on Fe4Mo8Na was established. The linear response range for H2O2 detection was 0.5-100 µM, and the detection limit was 0.143 µM. The linear response for ascorbic acid detection ranges from 0 to 750 µM with a detection limit of 1.07 µM. This study provides a new perspective for developing new nanozymes and expanding the sensing and detection application of nanozymes.

Bimetal loaded graphitic carbon nitride with synergistic enhanced peroxidase-like activity for colorimetric detection of p-phenylenediamine.

In recent years, great progress has been made on the study of nanozymes with enzyme-like properties. Here, bimetallic Fe and Ni nanoclusters were anchored on the nanosheets of nitrogen-rich layered graphitic carbon nitride by one-step pyrolysis at high temperature (Fe/Ni-CN). The loading content of Fe and Ni on Fe/Ni-CN is as high as 8.0%, and Fe/Ni-CN has a high specific surface area of 121.86 m2 g-1. The Fe/Ni-CN can effectively oxidize 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2, and exhibits efficient peroxidase-like activity, leading to a 17.2-fold increase compared to pure graphitic carbon nitride (CN). Similar to the natural horseradish peroxidase (HRP), the Fe/Ni-CN nanozyme follows catalytic kinetics. The Michaelis-Menten constant (Km) value of the Fe/Ni-CN nanozyme for TMB is about 8.3-fold lower than that for HRP, which means that the Fe/Ni-CN nanozyme has better affinity for TMB. In addition, the catalytic mechanism was investigated by combination of free radical quenching experiments and density-functional theory (DFT) calculations. The results show that the high peroxidase-like activity is due to the easy adsorption of H2O2 after bimetal loading, which is conducive to the production of hydroxyl radicals. Based on the extraordinary peroxidase-like activity, the colorimetric detection of p-phenylenediamine (PPD) was constructed with a wide linear range of 0.2-30 µM and a low detection limit of 0.02 µM. The sensor system has been successfully applied to the detection of residual PPD in real dyed hair samples. The results show that the colorimetric method is sensitive, highly selective and accurate. This study provides a new idea for the efficient enhancement of nanozyme activity and effective detection of PPD by a bimetallic synergistic strategy.

Portable alkaloid discrimination via nanozyme-mediated colorimetric paper-based sensor array integrated with smartphone detection.

A paper-based colorimetric sensor array mediated by a novel nanozyme (CuCo2O4) was developed using a screen-printing technology. The aim was to facilitate the identification of different kinds of alkaloids. Typically, three chromogenic substrates (3,3',5,5'-tetramethylbenzidine, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), and o-phenylenediamine) were selected as sensing elements, which can be catalyzed by a CuCo2O4 nanozyme with peroxidase-like activity to yield corresponding oxidized products, thereby inducing color changes. Owing to the varying inhibitory ability of different alkaloids on acetylcholinesterase (AChE), a decrease in choline (Ch) concentration occurs and subsequently results in the restoration of color within the units of sensor array. Color data can be transformed into hue information with a smartphone. The above color variations generated a unique "fingerprint" pattern on five alkaloids (berberine, palmatine, jatrorrhizine, eserine, and harmane), which can be successfully discriminated through linear discriminant analysis in the range 0.2 to 20 µM. Furthermore, the sensor arrays allowed successful discrimination of the above five alkaloids in Chinese herbal medicine samples and recognition of 22 blind samples. This work presents a novel nanozyme-based paper sensor array, which is a user-friendly and reliable platform for probing different alkaloids. In addition, the developed sensing strategy enables the identification of AChE-related diseases, positively contributing to the screening available of AD-associated drugs.

Ratiometric fluorescence and colorimetric strategies for assessing activity of butyrylcholinesterase in human serum using g-C3N4 nanosheets, silver ion and o-phenylenediamine.

Ratiometric fluorescence and colorimetric strategies for detecting activity of butyrylcholinesterase (BChE) in human serum were developed by using g-C3N4 nanosheets, silver ion (Ag+) and o-phenylenediamine (OPD) as chromogenic agents. The oxidation-reduction reaction of OPD and Ag+ generates 2,3-diaminophenazine (oxOPD). Under exciation at 370 nm, g-C3N4 nanosheets and oxOPD emit fluorescence at 440 nm (F440) and 560 nm (F560), respectively. Additionally, oxOPD exhibits quenching ability towards g-C3N4 nanosheets via photoinduced electron transfer (PET) process. Thiocholine (TCh), as a product of BChE-catalyzed hydrolysis reaction of butylthiocholine iodide (BTCh), can coordinate with Ag+ intensively, and consequently diminish the amount of free Ag+ in the testing system. Less amount of free Ag+ leads to less production of oxOPD, resulting in less fluorescence quenching towards g-C3N4 nanosheets as well as less fluorescence emission of oxOPD. Therefore, by using g-C3N4 nanosheets and oxOPD as fluorescence indicators, the intensity ratio of their fluorescence (F440/F560) was calculated and employed to evaluate the activity of BChE. Similarly, the color variation of oxOPD indicated by the absorbance at 420 nm (ΔA420) was monitored for the same purpose. These strategies were validated to be sensitive and selective for detecting BChE activity in human serum, with limits of detection (LODs) of 0.1 U L-1 for ratiometric fluorescence mode and 0.7 U L-1 for colorimetric mode.

Preparation of D-NCCDs and its application in fluorescent/colorimetric dual-mode discrimination of glutamine enantiomers.

A new type of carbon dots (D-NCCDs) was synthesized by 3, 5-diaminobenzoic acid, N,N-dimethyl-o-phenylenediamine, and D-cysteine. The morphology and structure of D-NCCDs were investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and FT-IR spectra, and the chirality was characterized by circular dichroism. In the presence of hydrogen peroxide, the fluorescence of D-NCCDs at 487 nm (λex = 410 nm) showed great discrimination ability towards glutamine enantiomers. The ratio of fluorescence intensity (F/F0) to the concentration of D-Gln showed good linearity in the range 0.5-10 mM, with a detection limits of 0.11 mM. Meanwhile, the color of the solution gradually changed from light yellow to yellow-brown. The UV-Vis absorption ratio (A/A0) at 410 nm showed good linearity with the concentration of D-Gln in the range 0.5 to 20 mM; the detection limit is 7.7 µM. But the fluorescence and absorbance of D-NCCDs showed no significant change after the addition of L-glutamine. Thus, fluorescence and colorimetry dual-mode discrimination of glutamine enantiomers was achieved. The fluorescence enantioselectivity of Gln (FL-Gln/FD-Gln) is 1.62, and the colorimetric enantioselectivity of Gln (AD-Gln/AL-Gln) is 2.14. The chiral discrimination mechanism of D-NCCDs to Gln enantiomers was also investigated systematically. This work not only can discriminate glutamine enantiomers with high sensitivity and convenience, but also offers a new strategy for preparing new dual mode chiral nanoprobes.

An epitope imprinted electrochemical sensor for highly sensitive and selective determination of prostate-specific antigen.

A simple method for highly selective and sensitive prostate-specific antigen (PSA) detection using a molecularly imprinted electrochemical sensor is presented. The sensor was developed through an epitope imprinted strategy combined with electrochemical measurement techniques. An epitope molecularly imprinted polymer (EMIP) film was constructed on a AuNPs-coated gold electrode surface through electropolymerization, utilizing the C-terminus epitope of PSA (KWIKDTIVANP) as the template molecular and o-phenylenediamine as the functional monomer. The characteristics of EMIP film were investigated by using a scanning electron microscope and electrochemical test methods, including electrochemical impedance spectroscopy and cyclic voltammetry. Key parameters such as electropolymerization cycles, elution and rebinding times, and the molar ratio of template molecular to functional monomer were systematically optimized. The sensor demonstrated a detection limit (LOD) of 0.31 fg/mL and exhibited an excellent linear response towards PSA concentration ranging from 1.0 fg/mL to 0.1 µg/mL. Furthermore, the EMIP sensor showed excellent selectivity against other biological macromolecules, such as bovine serum albumin, human serum albumin, alpha-fetoprotein, and carcinoembryonic antigen. With recoveries between 95.89 and 106.04% for PSA detection in human serums the EMIP/AuNPs/AuE electrochemical sensor showed great potential in real sample analysis.

A colorimetric and electrochemical dual-mode Hg2+ sensor utilizing oxidase-like activity arising from the combination of Hg2+ and palladium metal-organic framework@graphene.

Developing convenient and reliable methods for Hg2+ monitoring is highly important. Some precious metal nanomaterials with intriguing peroxidase-like activity have been used for highly sensitive Hg2+ detection. However, H2O2 must be added during these detections, which impedes practical applications of Hg2+ sensors due to its susceptible decomposition by environmental factors. Herein, we discovered that the combination of Hg2+ and palladium metal-organic framework@graphene (Pd-MOF@GNs) exhibits oxidase-like activity (OXD). In the absence of H2O2, this activity not only catalyzes the oxidation of chromogenic substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) or o-phenylenediamine (OPD) to produce a color change but also enhances the electrical signals during OPD oxidation. Based on these properties, an effective and convenient dual-mode colorimetric and electrochemical sensor for Hg2+ has been developed. The colorimetric and amperometric linear relationships for Hg2+ were 0.045 µM-0.25 mM and 0.020 µM-2.0 mM, respectively. The proposed strategy shows good recovery in real sample tests, indicating promising prospects for multiple environmental sample detection of Hg2+ without relying on H2O2. The colorimetric and electrochemical dual-mode Hg2+ sensor is expected to hold great potentials in applications such as environmental monitoring, rapid field detection, and integration into smartphone detection of Hg2+.