Photothermal-enhanced peroxidase-like activity of CDs/PBNPs for the detection of Fe3+ and cholesterol in serum samples

Tri-emissive red-green dye-encapsulated UiO-66-Ph as a white-light emission fluorescence sensor for Fe3+ and Cr2O72- detection in environmental water samples

Excessive inorganic ions in water sources can accumulate abnormally or be deficient in the human body, leading to serious health risks, such as liver and kidney damage or even cancer. Therefore, efficient and accurate detection of excessive inorganic ions in water is urgently needed. Using an in situ encapsulation method under solvothermal conditions, we develop a series of triple-emission fluorescent sensors, C6&RhB@UiO-66-Ph (C&R@U), by encapsulating green-emitting Coumarin 6 (C6) and red-emitting Rhodamine B (RhB) into a blue-emitting UiO-66-Ph MOF with 1,4-H2NDC as the ligand. Among them, C&R@U3 exhibits white-light emission with a CIE coordinate of (0.32, 0.32) and is used for the detection of Fe3+ ions and Cr2O72- ions in water. When the C&R@U3 fluorescent probe interacts with target ions, the three emission peaks of the probe are quenched due to the resonance energy transfer effect, resulting in significant shifts in its CIE coordinates compared to other ions. The fluorescence intensity of the C&R@U3 probe demonstrates excellent linearity with Fe3+ ion concentrations (0-0.6 mM) and Cr2O72- ion concentrations (0-0.1 mM), with detection limits of 0.71 μM and 16.9 nM, respectively. Experiments with real-world water samples and portable fluorescence test papers validate the practical applicability of C&R@U3, revealing its great potential in on-site inorganic ion detection. This work provides experimental basis and theoretical foundation for the development of new multifunctional fluorescent sensors, promoting the application of MOFs in environmental monitoring.

A novel tri-mode detection platform for ampicillin and drug resistance genes by CRISPR-driven luminescent nanozymes

The antibiotic residues pose significant risks for bacterial resistance. To address the practical requirements for rapid, accurate, and on-site detection of antibiotic residues and monitoring the abundance of associated resistance genes, we report a smartphone-integrated multi-mode platform. The platform is aimed to simultaneous, accurate, and visual quantitative detection of ampicillin (AMP) and β-lactam antibiotic resistance genes (blaTEM). Specifically, we developed a magnetically controlled fluorescence, colorimetric, and photothermal biosensor based on a magnetic separation unit (aminated modified complementary DNA chain (NH2-cDNA) loading on the surface of Ferrosoferric Oxide@polydopamine (Fe3O4@PDA, FP), FP@cDNA) and a signal unit (the aptamer nucleic acid chain modified by phosphate group linked to Prussian blue@UiO-66@manganese dioxide (PB@UiO-66@MnO2, PUM) through Zr-O-P bond, PUM@Apt), for the integrated detection of AMP and blaTEM. By utilizing complementary base pairing between FP@cDNA and PUM@Apt, along with precise aptamer recognition the AMP, we achieved the fluorescence quantitative detection of AMP by measuring the signal unit in the supernatant. Subsequently, the difference of signal units in colorimetric process leads to a varying conversion rate of oxidized 3,3',5,5'-Tetramethylbenzidine (oxTMB), enabling the output of colorimetric and photothermal signals. The competitive binding of aptamers permitting the determination of AMP in the range of 0-160 pM with a low detection limit (0.34 pM). Additionally, in the presence of blaTEM, the activated CRISPR/Cas12a indiscriminately cleaves the single-stranded portion of the FP@DNA@PUM complex obtained by magnetic separation. A PUM-based three-signal detection scheme was established for the sensitive determination of blaTEM with the limit of detection (LOD) of 1.03 pM. The integration of smartphone-assisted analysis broadens the potential of the platform for visual detection. Notably, the innovative platform, with its excellent stability, exhibits great potential as a simple yet robust approach for the simultaneously visually monitoring antibiotics and drug resistance genes, and holds promise in the field of kit development.

A ruthenium-nickel metal-organic framework incorporating 2,2'-bipyridine- 5,5'-dicarboxylic acid for dual-mode electrochemiluminescence-fluorescence detection of ferric ions

A novel, low-toxicity Ru-Ni-BPY metal-organic framework (MOF) nanomaterial was developed and a simple and sensitive dual-mode "on-off" ferric ions (Fe3+) sensing platform based on this material constructed. The dual-mode detection method enabled cross-validation of the electrochemiluminescence (ECL) and fluorescent (FL) signals, enhancing accuracy and effectively minimizing errors. In linear ranges of 0.005-10 μM and 0.078-10 μM, Fe3+ can dramatically quench the ECL and FL signals of the Ru-Ni-BPY MOF, with quenching rates of 91.42% and 91.31%, respectively, and detection limits of 0.1 nM and 9.3 nM, respectively. This ECL method not only achieved efficient detection of Fe3+ in rat brain microdialysis fluid but also successfully enabled real-time FL detection of Fe3+ in nude mice. Therefore, this platform has great potential for applications in environmental protection, life sciences, and early disease diagnosis.

B, N co-doped carbon dots as efficient nanozymes for colorimetric and fluorometric dual-mode detection of cholesterol

In this work, the B, N co-doped carbon dots (B, N-CDs) were synthesized via facile hydrothermal approach with 6-aminopyridine boronic acid as precursor. In addition to emitting intense blue luminescence when exposed to ultraviolet light, the prepared B, N-CDs displayed remarkable peroxidase-like activity, which could efficiently catalyze the oxidation of 3, 3', 5, 5' -tetramethylbenzidine (TMB) to blue ox-TMB in the presence of hydrogen peroxide (H2O2). Furthermore, the fluorescence intensity of B, N-CDs increased gradually upon the addition of H2O2. Since cholesterol oxidase (ChOx) can catalyze the oxidation of cholesterol to form H2O2, the as-prepared B, N-CDs was then used as both colorimetric and fluorometric sensors for the detection of cholesterol with detection limit of 0.87 and 2.31 μM, respectively. Finally, the dual-mode approach based on B, N-CDs was effectively utilized for detecting cholesterol levels in serum samples, proving the potential application of B, N-CDs in the field of biological assay.

Sensitive Dual-Signal ELISA Based on Specific Phage-Displayed Double Peptide Probes with Internal Filtering Effect to Assay Monkeypox Virus Antigen

The global spread of monkeypox has become a worldwide public healthcare issue. Therefore, there is an urgent need for accurate and sensitive detection methods to effectively control its spreading. Herein, we screened by phage display two peptides M4 (sequence: DPCGERICSIAL) and M6 (sequence: SCSSFLCSLKVG) with good affinity and specificity to monkeypox virus (MPXV) B21R protein. To simulate the state of the peptide in the phage and to avoid spatial obstacles of the peptide, GGGSK was added at the C terminus of M4 and named as M4a. Molecular docking shows that peptide M4a and peptide M6 are bound to different epitopes of B21R by hydrogen bonds and salt-bridge interactions, respectively. Then, peptide M4a was selected as the capture probe, phage M6 as the detection probe, and carbonized polymer dots (CPDs) as the fluorescent probe, and a colorimetric and fluorescent double-signal capture peptide/antigen/signal peptide-displayed phage sandwich ELISA triggered by horseradish peroxidase (HRP) through a simple internal filtration effect (IFE) was constructed. HRP catalyzes H2O2 to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue oxidized TMB, which can further quench the fluorescence of CPDs through IFE, enabling to detect MPXV B21R in colorimetric and fluorescent modes. The proposed simple immunoassay platform shows good sensitivity and reliability in MPXV B21R detection. The limit of detection for colorimetric and fluorescent modes was 27.8 and 9.14 pg/mL MPXV B21R, respectively. Thus, the established double-peptide sandwich-based dual-signal immunoassay provides guidance for the development of reliable and sensitive antigen detection capable of mutual confirmation, which also has great potential for exploring various analytical strategies for other respiratory virus surveillance.

Paper test strip for fluorescence detection of iron ion based on nitrogen, zinc and copper codoped carbon dots

In this study, a test strip for fluorometric analysis of iron ion (Fe3+) was constructed based on nitrogen, zinc and copper codoped carbon dots (NZC-CDs) as fluorescence probes. NZC-CDs were synthesized by hydrothermal method. The morphology, size, components, crystal state and optical properties of NZC-CDs were characterized by transmission electron microscope (TEM), Fourier-transform infrared (FT-IR), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), UV-vis absorption and fluorescence spectroscopy techniques, respectively. NZC-CDs exhibited bright blue fluorescence under UV lamp with a quantum yield at 17.76%. The fluorescence of NZC-CDs was quenched by Fe3+possibly due to the static quenching. The possible fluorescence quenching mechanism was also discussed. The quenching fluorescence was linear with the concentration of Fe3+in the range of 2.5-400μM with a low detection limit of 0.5μM. For the convenient detection, the test strips based on filter paper were employed for Fe3+assay. Moreover, the present approach was successfully applied in the determination of Fe3+in real samples including black fungus, duck blood and pork liver. The sensing method had the potential application in more food analysis.

Zinc pyrovanadate nanorods with excellent peroxidase-like activity at physiological pH for the colorimetric assay of H2O2 and epinephrine

Exploring highly active peroxidase mimics at physiological pH is important for the construction of efficient and convenient colorimetric sensing platforms for detecting small biomolecules. In this work, prepared zinc pyrovanadate (Zn₃V₂O₇(OH)₂·2H₂O) nanorods exhibit excellent peroxidase-like activity, which is verified by the fast oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue product (oxTMB) by H₂O₂ at physiological pH (pH = 7) in 2 min. In addition, the catalytic behaviors of Zn₃V₂O₇(OH)₂·2H₂O as a peroxidase-like nanozyme conform to the Michaelis-Menten equation. Scavenger experiments prove that the catalytic activity of Zn₃V₂O₇(OH)₂·2H₂O is ascribed to ˙O₂^- radicals generated in the process of catalysis. Based on the peroxidase-like activity of the Zn₃V₂O₇(OH)₂·2H₂O nanozyme, a fast and convenient colorimetric sensor has been constructed to detect H₂O₂ and epinephrine (EP) under physiological pH. The detection limit of EP is as low as 0.26 μM. In addition, the feasibility of the proposed sensor has been validated to detect H₂O₂ in milk and EP in serum.

The study of a novel high selectivity pyrenyl-based fluorescence probe with aggregation-induced emission characteristics for Fe3+ detection designed by a structure modulation strategy

The past decades have witnessed the feat of fluorescent probes for Fe³⁺ detection, where eliminating the interference by other metal ions plays a pivotal role in its detection by probes in complex environments. Herein, by taking advantage of the substituent effects, the electron-withdrawing group (EWG) -CF₃ and electron-donating group (EDG) -CH₃ were introduced to 2-(1-pyrenyl)pyridine (pypyr) to prepare two turn-off fluorescence probes, 5-trifluoromethyl-2-(1-pyrenyl)pyridine (pypyr-CF3) and 5-methyl-2-(1-pyrenyl)pyridine (pypyr-CH3). Intriguingly, both probes displayed novel aggregation-induced emission (AIE) characteristics in MeCN/H₂O mixtures and the size and morphology of the aggregated particles were studied via DLS and TEM. By the modulation strategy, pypyr-CF3 can detect Fe³⁺ in the presence of 29 different metal ions without interference. Comparatively, pypyr-CH3 experienced serious interference from other metal ions such as Hg²⁺ and Zr⁴⁺. Besides, pypyr-CF3 not only demonstrated a higher photoluminescence quantum yield (PLQY) of 65.25% and wider pH adaptability but is also capable of Fe³⁺ detection over a wide pH range of 2-11 with a short response time (5 seconds). A plausible quenching mechanism based on the inner filter effect has also been demonstrated. More importantly, the versatile applications of pypyr-CF3, such as the quantitative analysis of Fe³⁺ in actual water samples, anti-forgery ink, fingerprint identification, etc., further corroborate its superb capabilities. This study aims to lend concrete support to the design and selectivity modulation of probes.

Colorimetric biosensor for visual determination of Golgi protein 73 based on reduced graphene oxide-carboxymethyl chitosan-Hemin/platinum@palladium nanozyme with peroxidase-like activity

A Golgi protein 73 (GP73) colorimetric biosensor based on the reduced graphene oxide-carboxymethyl chitosan-hemin/platinum@palladium nanoparticles (RGO-CMCS-Hemin/Pt@Pd NPs) with peroxidase-like activity was constructed. The RGO-CMCS-Hemin/Pt@Pd NPs with high peroxidase-like activity were successfully synthesized under mild conditions. Then, the aminylated GP73 aptamer (Apt) was bound to the RGO-CMCS-Hemin/Pt@Pd NPs to form the recognition probe. Another unmodified GP73 aptamer (AptI) was served as the capture probe. In the presence of target GP73, the capture probe and the recognition probe specifically bind to GP73 and form a RGO-CMCS-Hemin/Pt@Pd NP-Apt/GP73/AptI sandwich-type structure, which can oxidase the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB in the presence of H₂O₂. GP73 detection was achieved by measuring the peak UV absorption at 652 nm. Under the optimum conditions, the GP73 concentration was linearly related to the absorbance intensity in the range 10.0-110.0 ng/mL, and the limit of detection (LOD) was 4.7 ng/mL. The proposed colorimetric biosensor was successfully applied to detect GP73 in spiked human serum samples with recoveries of 98.2-107.0% and RSDs of 1.90-5.44%, demonstrating the excellent potential for highly sensitive GP73 detection in clinical detection. A colorimetric biosensor for visual determination of GP73 based on RGO-CMCS-Hemin/Pt@Pd NPs nanozyme with peroxidase-like activity was designed. The GP73 biosensor responses linearly from 10.0-110.0 ng/mL with LOD of 4.7 ng/mL, and shows acceptable specificity and good recovery.

Fluorescent Biosensor Based on Hairpin DNA Stabilized Copper Nanoclusters for Chlamydia trachomatis Detection

Chlamydia trachomatis (C. trachomatis) is a kind of intracellular parasitic microorganism, which can causes many diseases such as trachoma. In this strategy, a specific hairpin DNA with the probe loop as specific regions to recognize C. trachomatis DNA with strong affinity was designed, and its stem consisted of 24 AT base pairs as an effective template for hairpin DNA-CuNCs formation. In the absence of C. trachomatis DNA, the detection system showed strong orange fluorescence emission peaks at 606 nm. In the presence of C. trachomatis DNA, the conformation of DNA probe changed after hybridizing with C. trachomatis DNA. Then, the amount of hairpin DNA-CuNCs was reduced and resulted in low fluorescence emission. C. trachomatis DNA displayed a significant inhibitory effect on the synthesis of fluorescent hairpin DNA-CuNCs due to the competition between C. trachomatis DNA and the specific hairpin DNA. Under the optimal experimental conditions, different concentrations of C. trachomatis were tested and the results showed a good linear relationship in the range of 50 nM to 950 nM. Moreover, the detection limit was 18.5 nM and this detection method possessed good selectivity. Finally, the fluorescent biosensor had been successfully applied to the detection of C. trachomatis target sequence in HeLa cell lysate, providing a new strategy for the detection of C. trachomatis.