Peptide-RNA complexation-induced fluorescence "turn on" displacement assay for the recognition of small ligands targeting HIV-1 RNA

Coordination-Based Site-Specific Labeling Strategy for Electrogenerated Chemiluminescence Biosensing of Matrix Metalloproteinase 2

Matrix metalloproteinase 2 (MMP-2) is an important biomarker for some diseases. Herein, one first-case coordination-based site-specific labeling strategy is proposed for electrogenerated chemiluminescence (ECL) biosensing of MMP-2 by employing an iridium(III) solvent complex as a signal reagent and a histidine (His)-containing peptide as a molecular recognition substrate. One ECL probe was prepared via coordination labeling of the His-containing peptide with one iridium(III) solvent complex ([(3-(2-pyridyl)benzoic acid)2Ir(DMSO)Cl], Ir1-DMSO). High ECL efficiency and good cleavage ability by MMP-2 were obtained for the ECL probe. By combining the high sensitivity of the ECL method, the good specificity of the peptide, and the simpleness of the magnetic bead-based assay, one "cleavage-magnetic enrichment type" ECL biosensing method was developed to detect MMP-2. MMP-2 can be sensitively detected in the linear range of 1.0-10 ng/mL with a limit of quantification of 1.0 ng/mL and a limit of detection of 0.3 ng/mL. Moreover, the ECL biosensing method was successfully applied for the determination of MMP-2 in serum samples with recoveries from 98.0% ± 8.0% to 108.0% ± 6.0%. Further, high affinity (Kd = 0.11 nM) was obtained for the Ir1-DMSO-labeled His-containing peptide and MMP-2. This work may pave the way for the labeling of His-containing biomolecules with an iridium(III) solvent complex and provides a promising method in point-of-care testing of MMP-2.

Electrochemical detection of FTO with N3-kethoxal labeling and MazF cleavage

N6-Methyladenosine (m6A) is a prevalent modification in eukaryotic mRNAs and is linked to various human cancers. The fat mass and obesity-associated protein (FTO), a key m6A demethylase, is crucial in m6A regulation, affecting many biological processes and diseases. Detecting FTO is vital for clinical and research applications. Our study leverages the specific cleavage properties of the MazF endoribonuclease to design an electrochemical method with signal amplification guided by streptavidin-horseradish peroxidase (SA-HRP), intended for FTO detection. Initially, the compound N3-kethoxal is employed for its reversible tagging ability, selectively attaching to guanine (G) bases. Subsequently, dibenzocyclooctyne polyethylene glycol biotin (DBCO-PEG4-Biotin), is introduced through a reaction with N3-kethoxal. HRP is then employed to catalyze the redox system to enhance the current response further. A promising linear correlation between the peak current and the FTO concentration was observed within the range of 7.90 × 10-8 to 3.50 × 10-7 M, with a detection limit of 5.80 × 10-8 M. Moreover, this method assessed the FTO inhibitor FB23's inhibitory effect, revealing a final IC50 value of 54.73 nM. This result aligns with the IC50 value of 60 nM obtained through alternative methods and is very close to the values reported in the literature. The study provides reference value for research into obesity, diabetes, cancer, and other FTO-related diseases, as well as for the screening of potential therapeutic drugs.

Electrogenerated Chemiluminescence Biosensor for Quantization of Matrix Metalloproteinase-3 in Serum via Target-Induced Cleavage of Oligopeptide

A highly sensitive and selective electrogenerated chemiluminescence (ECL) biosensor was developed for the determination of matrix metalloproteinase 3 (MMP-3) in serum via the target-induced cleavage of an oligopeptide. One ECL probe (named as Ir-peptide) was synthesized by covalently linking a new cyclometalated iridium(III) complex ([(3-pba)2Ir(bpy-COOH)](PF6)) (3-pba = 3-(2-pyridyl) benzaldehyde, bpy-COOH = 4'-methyl-2,2'-bipyridine-4-carboxylic acid) with an oligopeptide (CGVPLSLTMGKGGK). An ECL biosensor was fabricated by firstly casting Nafion and gold nanoparticles (AuNPs) on a glassy carbon electrode and then self-assembling both of the ECL probes, 6-mercapto-1-hexanol and zwitterionic peptide, on the electrode surface, from which the AuNPs could be used to amplify the ECL signal and Ir-peptide could serve as an ECL probe to detect the MMP-3. Thanks to the MMP-3-induced cleavage of the oligopeptide contributing to the decrease in ECL intensity and the amplification of the ECL signal using AuNPs, the ECL biosensor could selectively and sensitively quantify MMP-3 in the concentration range of 10-150 ng·mL-1 and with both a limit of quantification (26.7 ng·mL-1) and a limit of detection (8.0 ng·mL-1) via one-step recognition. In addition, the developed ECL biosensor showed good performance in the quantization of MMP-3 in serum samples, with a recovery of 92.6% ± 2.8%-105.6% ± 5.0%. An increased level of MMP-3 was found in the serum of rheumatoid arthritis patients compared with that of healthy people. This work provides a sensitive and selective biosensing method for the detection of MMP-3 in human serum, which is promising in the identification of patients with rheumatoid arthritis.

Chemical derivatization strategies for enhancing the HPLC analytical performance of natural active triterpenoids

Triterpenoids widely exist in nature, displaying a variety of pharmacological activities. Determining triterpenoids in different matrices, especially in biological samples holds great significance. High-performance liquid chromatography (HPLC) has become the predominant method for triterpenoids analysis due to its exceptional analytical performance. However, due to the structural similarities among botanical samples, achieving effective separation of each triterpenoid proves challenging, necessitating significant improvements in analytical methods. Additionally, triterpenoids are characterized by a lack of ultraviolet (UV) absorption groups and chromophores, along with low ionization efficiency in mass spectrometry. Consequently, routine HPLC analysis suffers from poor sensitivity. Chemical derivatization emerges as an indispensable technique in HPLC analysis to enhance its performance. Considering the structural characteristics of triterpenoids, various derivatization reagents such as acid chlorides, rhodamines, isocyanates, sulfonic esters, and amines have been employed for the derivatization analysis of triterpenoids. This review comprehensively summarized the research progress made in derivatization strategies for HPLC detection of triterpenoids. Moreover, the limitations and challenges encountered in previous studies are discussed, and future research directions are proposed to develop more effective derivatization methods.

Ligand "switching on" fluorescence of HIV-1 RNA-templated copper nanoclusters for ligand-RNA interaction assays

Ligand-RNA interaction assay provides the basis for developing new RNA-binding small molecules. In this study, fluorescent copper nanoclusters (CuNCs) were first prepared using two kinds of HIV-1 RNA targets, rev-responsive element (RRE) and transactivator response element (TAR) RNA, as new templates, and it was found that the fluorescence of the single RNA-templated CuNCs was negligible. Using neomycin as a model drug, the fluorescence could be augmented (approximately 6 times) for the neomycin/RNA-templated CuNCs. Thus, a novel method was developed for ligand-RNA interactions by observing the fluorescence changes in CuNCs prepared using RNA before and after the addition of ligands. The preparation parameters of neomycin/RNA-CuNCs were optimized. The as-prepared CuNCs were characterized using UV-vis spectroscopy, fluorescence spectroscopy, and high-resolution transmission electron microscope. Circular dichroism spectral analysis showed that RRE and TAR were inclined to form a double-stranded structure after interaction with neomycin, which was more conducive to the formation of CuNCs. The interactions of neomycin and three test drugs (amikacin, gentamicin, and tobramycin) with RNA were investigated using the proposed method, and the binding constants and number of binding sites were obtained through theoretical calculations. This study provides a novel approach for ligand-RNA interaction assays.

Electrochemiluminescence bioassay with anti-fouling ability for determination of matrix metalloproteinase 9 secreted from living cells under external stimulation

An electrochemiluminescence (ECL) bioassay with high sensitivity and anti-fouling ability was developed for determination of matrix metalloproteinase 9 (MMP-9) secreted from living cells under external stimulation. A peptide with sequence of CLGRMGLPGK and a new cyclometalated iridium(III) complex bearing carboxyl group, (pq)2Ir(dcbpy) (pq = 2-phenylquinoline, dcbpy = 2,2'-bipyridyl-4,4'-dicarboxyli acid, abbreviated as Ir) were employed as molecular recognition substrate and ECL emitter, respectively. The peptide was labelled with the Ir to form Ir-peptide as ECL probe. Ir-peptide was self-assembled onto Nafion and gold nanoparticles (AuNPs) modified glassy carbon electrode (AuNPs/Nafion/GCE) and then both of 6-mercapto-1-hexanol (MCH) and zwitterionic peptide as blocking reagents were co-assembled on Ir-peptide/AuNPs/Nafion/GCE to form an anti-fouling ECL peptide-based biosensor. MMP-9 can be quantified in the range 1.0-50 ng·mL-1 with a detection limit of 0.50 ng·mL-1 based on the decreased ECL intensity. Relative standard derivation was 2.3% for six fabricated anti-fouling ECL peptide-based biosensors after reaction with 50 ng·mL-1 MMP-9. The anti-fouling ECL peptide-based biosensor can be used to monitor MMP-9 secreted from living cells under external stimulation. 96.0%-108.0% of recoveries were obtained in 60-diluted cell culture media. This study demonstrates that the ECL biosensor by the combination of iridium(III) complex-based sensitive ECL method and the anti-fouling interface provides a promising way for the determination of MMP-9 in biological sample, which is viable in clinical diagnosis and point-of-care test of protease.