Sensitive detection of dipeptidyl peptidase based on DNA-peptide conjugates and double signal amplification of CHA and DNAzymes

Dipeptidyl peptidase IV (DPPIV) is an enzyme belonging to the type II transmembrane serine protease family that has gained wide interest in the fields of hematology, immunology, and cancer biology. Moreover, DPPIV has emerged as a promising target for therapeutic intervention in type II diabetes. Due to its biological limitations, traditional strategies cannot meet the requirements of low abundance DPPIV analysis in complex environments. In this work, combining the high programmability of DNA and the chemical diversity of peptides, we designed DNA-peptide conjugates that can be specifically recognized, polypeptides as specific substrates for target DPPIV and DNA probes as primers for catalytic hairpin assembly (CHA), recycling a large amount of DNAzymes by triggering CHA amplification. The DNAzyme substrate modified with the FAM fluorescent group was immobilized on the surface of gold nanoparticles by S-Au chemical bonds to form a signal output probe. The DNAzymes enzyme cleaved the substrate of the signal outputs probe, yielding a double-amplified fluorescence signal. This method has a detection limit as low as 0.18 mU mL-1 and a linear range of 0-5 mU mL-1 in serum samples, showing high stability and good potential for practical applications.

Visualizing Dipeptidyl Peptidase-IV with an Advanced Non-π-Conjugated Fluorescent Probe for Early Thyroid Disease Diagnosis

Early detection and effective treatment of thyroid cancer are vital due to the aggressiveness and high mortality rate of the cancer. Nevertheless, the exploration of dipeptidyl peptidase-IV (DPP-IV) as a biomarker for thyroid diseases has not been widely conducted. In this study, we developed a novel non-π-conjugated near-infrared fluorescent probe, MB-DPP4, specifically designed to visualize and detect endogenous DPP-IV. Traditional DPP-IV-specific fluorescent probes rely primarily on the intramolecular charge transfer mechanism. For this reason, these probes are often hampered by high background levels that can inhibit their ability to achieve a fluorescence turn-on effect. MB-DPP4 successfully surmounts several drawbacks of traditional DPP-IV probes, boasting unique features such as exceptional selectivity, ultrahigh sensitivity (0.29 ng/mL), innovative structure, low background, and long-wavelength fluorescence. MB-DPP4 is an "off-on" chemosensor that exhibits strong fluorescence at 715 nm and releases a methylene blue (MB) fluorophore upon interacting with DPP-IV, resulting in a visible color change from colorless to blue. Given these remarkable attributes, MB-DPP4 shows great promise as a versatile tool for advancing research on biological processes and for evaluating the physiological roles of DPP-IV in living systems. Finally, we conducted a comprehensive investigation of DPP-IV expression in human serum, urine, thyroid cells, and mouse thyroid tumor models. Our findings could potentially establish a foundation for the early diagnosis and treatment of thyroid diseases.

Optical substrates for drug-metabolizing enzymes: Recent advances and future perspectives

Drug-metabolizing enzymes (DMEs), a diverse group of enzymes responsible for the metabolic elimination of drugs and other xenobiotics, have been recognized as the critical determinants to drug safety and efficacy. Deciphering and understanding the key roles of individual DMEs in drug metabolism and toxicity, as well as characterizing the interactions of central DMEs with xenobiotics require reliable, practical and highly specific tools for sensing the activities of these enzymes in biological systems. In the last few decades, the scientists have developed a variety of optical substrates for sensing human DMEs, parts of them have been successfully used for studying target enzyme(s) in tissue preparations and living systems. Herein, molecular design principals and recent advances in the development and applications of optical substrates for human DMEs have been reviewed systematically. Furthermore, the challenges and future perspectives in this field are also highlighted. The presented information offers a group of practical approaches and imaging tools for sensing DMEs activities in complex biological systems, which strongly facilitates high-throughput screening the modulators of target DMEs and studies on drug/herb‒drug interactions, as well as promotes the fundamental researches for exploring the relevance of DMEs to human diseases and drug treatment outcomes.

A new fluorescence probe for detection of Cu+2 in blood samples: Circuit logic gate

A Fluorescence probe was designed based on 8-hydroxyquinoline chitosan silica precursor (HQCS) for selective detection of Al3+, Cu2+. The HQCS has no observable fluorescence signal, but after the addition of Al3+, a huge fluorescence signal appeared, and the selective quenching was absorbed after the addition of Cu2+. The effect of other different cations, including Cu2+, Mg2+, Ca2+, Pb2+, Zn2+, Hg2+, Ag+, Fe3+, and K+ was studied. The addition of Cu2+ to the probe (HQCSAL) decreased the fluorescence very repeatable, and the variation of the fluorescence vs. Cu2+ was monotonic and linear. Therefore, the prepared probe was used to determine Cu2+ ions in real samples. The mechanism of fluorescence variation by adding cations to the probe solution was studied using the Stern-Volmer equation. Under the optimum conditions, the linear range and detection limit were 3.5-31 μM and 1 μM, respectively. The probe accuracy on the copper determination in the blood and tap waters was comparable to the ICP-OES results. The circuit logic gate mimic was designed for the fluorescence behavior of the probe constituents.

Long-Wavelength Ratiometric Fluorescent Probe for the Early Diagnosis of Diabetes

Diabetes is a metabolic disease caused by high blood sugar. Patients are often suffering from high blood pressure and arteriosclerosis, which may even evolve into liver disease, kidney disease, and other diabetic complications. Dipeptide peptidase IV (DPP-IV) plays an important role in regulating blood sugar levels and is one of the targets for the diagnosis and treatment of diabetes. Here, a long-wavelength ratiometric fluorescent probe DCDHFNH₂-dpp4 for detecting DPP-IV was designed and synthesized. DCDHFNH₂-dpp4 was used to detect DPP-IV in healthy, tumor-bearing, and diabetic mice, and only diabetic mice showed strong fluorescence signals. In organ imaging, it is found that DPP-IV is relatively enriched in the liver of diabetic mice. In addition, probe DCDHFNH₂-dpp4 also exhibited a significant ratiometric fluorescence signal in the serum of diabetic mice. Therefore, the fluorescent probe DCDHFNH₂-dpp4 has shown outstanding potential in the early diagnosis of diabetes, and DCDHFNH₂-dpp4 is hopeful to be applied to actual clinical medicine.

A dual-channel chemosensor based on 8-hydroxyquinoline for fluorescent detection of Hg2+ and colorimetric recognition of Cu2

A novel dual-channel chemosensor, 7-allylquinolin-8-ol (AQ), was synthesized based on 8-hydroxyquinoline for selective fluorescence detection of Hg²⁺ and colorimetric recognition of Cu²⁺. The chemosensor reacted with Hg²⁺ and generated a new Hg-containing compound with significantly enhanced fluorescence, which turned from faint blue to strong green. Further experiments indicated that AQ could be used to quantitatively detect Hg²⁺ via fluorescence spectroscopy with a low detection limit (2.1 nM). The good reversibility of the synthesized chemosensor was also demonstrated using NaBH₄. Moreover, AQ was successfully used for the detection of Cu²⁺ through the formation of a stable coordination compound, which exhibited an ultraviolet-visible (UV-Vis) ratiometric change, while its color changed from colorless to pale yellow under natural light. Additional experiments using various Cu²⁺ concentrations showed that the developed chemosensor could be further employed for the quantitative ratiometric estimation of Cu²⁺ by UV-Vis.

A novel electrochemical sensor based on molecularly imprinted polymer modified hollow N, S-Mo2C/C spheres for highly sensitive and selective carbendazim determination

A novel electrochemical sensor based on nitrogen and sulfur doped hollow Mo₂C/C spheres (N, S-Mo₂C) and molecularly imprinted polymer (MIP) was proposed for carbendazim (CBD) determination. The N, S-Mo₂C were prepared by first nitrogen and sulfur doping via one-pot method and subsequent carbonization at high temperature. A film of MIP was then fabricated in situ on the N, S-Mo₂C surface by electropolymerization, with CBD acting as template molecule and o-phenylenediamine as functional monomer. The N, S-Mo₂C were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and electrochemical behaviors of CBD on differently modified electrodes were explored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Under the optimal conditions, a calibration curve of current shift versus the logarithm of CBD concentration was obtained in the range of 1×10^-12 ∼ 8×10^-9 M with a detection limit of 6.7×10^-13 M (S/N=3). Moreover, the proposed sensor exhibited favorable stability and selectivity, and was applied to analyze pesticide residues in fruits and vegetables with decent accuracy.