Gold nanoparticle extraction followed by o-phthaldialdehyde derivatization for fluorescence sensing of different forms of homocysteine in plasma

O-phthalaldehyde assisted surface enhanced Raman spectroscopy selective determination of trace homocysteine in serum

High plasma homocysteine (Hcy) levels may indicate cardiovascular disease. However, sensitive and selective determination of Hcy remains a major challenge. Herein, we present a sensing strategy for Hcy by surface enhanced Raman scattering (SERS) method along with a specific reaction of o-phthalaldehyde (OPA) and Hcy. The obtained adduct 2-(1-carboxyl-3-thiopropyl)-1-isoindolinone (Hcy-OPA) can be directly detected by SERS using gold nanoparticles (Au NPs) as the substrate. The developed SERS method displays superior sensitivity (low detection limit of 2.50 × 10^-12 mol L^-1) with a broad linear range (5.00 × 10^-10 -5.00 × 10^-6 mol L^-1). As a proof of real application, it can be used to detect Hcy in bovine serum samples with a concentration as low as 5.00 × 10^-9 mol L^-1, which is free from the interference of the other amino acids and glutathione.

A novel and simple imidazo[1,2-a]pyridin fluorescent probe for the sensitive and selective imaging of cysteine in living cells and zebrafish

Cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) play many crucial physiological roles in organisms. Their abnormal levels can cause and indicate various diseases. In the present study, a small-molecule fluorescent probe 2-(imidazo[1,2-a]pyridin-2-yl)phenyl acrylate (IPPA) was designed, synthesized and characterized by NMR, FT-IR and HRMS. IPPA can selectively detect Cys over other analytes because of an approximately 76 times enhancement in fluorescence intensity. The limit of detection of IPPA for Cys was 0.33 μM. The pseudo-first-order rate constant of the reaction between IPPA and Cys was approximately 10 times that of the reaction between IPPA and Hcy (KCys 3.18 × 10-3 S-1vs KHcy 4.92 × 10-4 S-1), indicating that Cys can be distinguished from Hcy. In addition, IPPA exhibits strong anti-interference ability, small molecular weight, high efficiency, low toxicity and good cell permeability. It was successfully used in imaging HepG2 cells and zebrafish. The fluorescence response of IPPA for calf serum are powerful proofs for practical application. Therefore, IPPA has high potential for bioassay applications.

Electrophoretic analysis of polyamines in exhaled breath condensate based on gold-nanoparticles microextraction coupled with field-amplified sample stacking

In this work, citrate-capped gold-nanoparticles (citrate-AuNPs) have been firstly used for selective extraction of trace polyamines, putrescine (Put) and cadaverine (Cad), followed by field-amplified sample stacking (FASS) coupled with capillary electrophoresis and capacitively coupled contactless conductivity detection (FASS-CE-C⁴D). Put and Cad were extracted by electrostatic attractions between the amine group of the polyamines and the citrate ligands adsorbed on the surfaces of AuNPs. AuNPs microextraction (AuNPs-ME) effectively shortened preparation time (50 min) by introducing ultrasound, and the required sample extraction volume was only 1 mL. Furthermore, a synergistic enrichment strategy based on off-line AuNPs-ME and on-line FASS significantly improved the detection sensitivity, making the enrichment factors up to 1726-1887 times. Under the optimum conditions, Put and Cad could be well separated from the potential coexisting substances and then directly determined by CE-C⁴D without derivatization. Due to its low sample consumption, high sensitivity (LODs: 0.070-0.17 ng mL^-1), and acceptable recoveries (90-105%), this AuNPs-ME/FASS-CE-C⁴D method provides a rapid, economical and eco-friendly approach for direct determination of polyamines in human exhaled breath condensate, and has potential application prospects in preliminary noninvasive diagnosis of oral and respiratory inflammation.

High-Efficiency Recognition and Identification of Disulfide Bonded Peptides in Rat Neuropeptidome Using Targeted Electron Transfer Dissociation Tandem Mass Spectrometry

The main goal of the present study is to develop a method to recognize and identify endogenous intrachain disulfide bonded peptide, which are rarely sequenced in current peptidomics studies. In order to achieve highly efficient detection of these peptides in a neuropeptidome analysis, we alkylated the peptides, mined the raw mass spectrometry data, and then recognized the candidates of untreated disulfide bonded peptides from unalkylated peptide extracts. After removing more than 90% features, targeted electron transfer dissociation fragmentation was performed for detecting and fragmenting disulfide bonded peptides, and even most of them were present in low abundance in the original sample. Diverse endogenous disulfide bonded peptides were then detected and sequenced, opening up new perspectives for comprehensively understanding the response of a neuropeptidome.

Recent advances in thiol and sulfide reactive probes

Because of the biological relevance of thiols and sulfides such as cysteine, homocysteine, glutathione and hydrogen sulfide, their detection has attracted a great deal of research interest. Fluorescent probes are emerging as a new strategy for thiol and hydrogen sulfide analysis due to their high sensitivity, low cost, and ability to detect and image thiols in biological samples. In this short review, we have summarized recent advances in the development of thiol and hydrogen sulfide reactive fluorescent probes. These probes are compared and contrasted with regard to their designing strategies, mechanisms, photophysical properties, and/or reaction kinetics. Biological applications of these probes are also discussed.

Determination of cysteine, homocysteine, cystine, and homocystine in biological fluids by HPLC using fluorosurfactant-capped gold nanoparticles as postcolumn colorimetric reagents

We have demonstrated for the first time the suitability of fluorosurfactant-capped spherical gold nanoparticles as HPLC postcolumn colorimetric reagents for the direct assay of cysteine, homocysteine, cystine, and homocystine. The success of this work was based on the use of an on-line tris(2-carboxyethyl)phosphine reduction column for cystine and homocystine. Several parameters affecting the separation efficiency and the postcolumn colorimetric detection were thoroughly investigated. Under the optimized conditions, cysteine, homocysteine, cystine, and homocystine in human urine and plasma samples were determined. Detection limits for cysteine, homocysteine, cystine, and homocystine ranged from 0.16-0.49 μM. The accuracy in terms of recoveries ranged between 94.0-102.1%. This proposed method was rapid, inexpensive, and simple.