Quantitation of sulfur-containing amino acids, homocysteine, methionine and cysteine in dried blood spot from newborn baby by HPLC-fluorescence detection

A fluorescein-gold nanoparticles probe based on inner filter effect and aggregation for sensing of biothiols

Cysteine (Cys), homocysteine (HCys) and glutathione (GSH) are sulfhydryl-containing amino acids known as biothiols being able to bind to gold nanoparticles (AuNPs) via sulfhydryl group, resulting in the aggregation of AuNPs. Owning to their inner filter effect, AuNPs can weaken or even quench the fluorescence of fluorescein. However, the introduction of biothiols to fluorescein-AuNPs leads to the recovery of fluorescein fluorescence. Thus, a simple and reliable turn on fluorescence method was developed for monitoring biothiols with fluorescein-AuNPs as a probe. Several factors, including AuNPs concentration, pH value and incubation time, which might influence the fluorescence reclamation of fluorescein-AuNPs probe, were optimized by taking Cys as an example at room temperature. Under the optimal conditions, sensitive sensing of Cys, HCys and GSH was achieved. The detection limits for Cys, GSH, and HCys were 0.027, 0.023, and 0.030μΜ, respectively. This method was used to the determination of Cys in human serum samples with high precision and accuracy, indicating the potential of the method in practical applications with simple operation, good accuracy and high sensitivity.

A far-red FRET fluorescent probe for ratiometric detection of l-cysteine based on carbon dots and N-acetyl-l-cysteine-capped gold nanoparticles

A novel far-red fluorescence resonance energy transfer (FRET) fluorescent probe for ratiometric detection of l-cysteine (l-Cys) has been designed. The system was established a FRET assembly by positively charged carbon dots (CDs) and negatively charged N-acetyl-l-cysteine capped gold nanoparticles (NAC-AuNPs). The fluorescence of CDs at 539 nm could be effectively quenched in the presence of NAC-AuNPs owing to FRET process, while the emission of NAC-AuNPs at 630 nm was appeared. Subsequently, the interactions between l-Cys and NAC-AuNPs resulted in the decreased emission intensity of NAC-AuNPs, but the emission intensity of CDs kept almost constant due to the continuous FRET efficiency. The ratio of emission intensities at 539 and 630 nm (I₅₃₉/I₆₃₀) exhibited a linear correlation to the l-Cys concentration in the range of 1.0-110 μM with the detection limit of 0.16 μM. Moreover, this far-red ratiometric sensor also revealed excellent selectivity toward l-Cys over other amino acids, which showed very high potential in the practical application for diagnosing of cysteine-related disease.

A photoelectrochemical sensing strategy based on single-layer MoS2 modified electrode for methionine detection

MoS₂, a typical transition metal disulfide, is widely used in the photoelectrochemical (PEC) sensor construction. In general, MoS₂ based PEC sensor are "signal-on" strategies. Surprisingly, we discovered that the PEC response of MoS₂ was quenched by methionine greatly. Based on this discovery, a reduction PEC sensing strategy utilized MoS₂ modified electrode for methionine detection was fabricated for the first time. Experimental factors, such as, bias potential, volume of MoS₂ and pH were studied. Under optimized conditions, the decreased intensity of the photocurrent signal was proportional to the logarithmic value of methionine concentrations from 0.1 nM to 1 μM with the detection limit of 0.03 nM. Moreover, this method exhibited good performance of excellent selectivity. And it showed potential applications in the practical determination of methionine in real-life sample. This strategy not only expands the PEC detection method but also provides a simple, rapid response, good selectivity and high sensitivity way to detect methionine.

Thermal Degradation of Small Molecules: A Global Metabolomic Investigation

Thermal processes are widely used in small molecule chemical analysis and metabolomics for derivatization, vaporization, chromatography, and ionization, especially in gas chromatography mass spectrometry (GC/MS). In this study the effect of heating was examined on a set of 64 small molecule standards and, separately, on human plasma metabolite extracts. The samples, either derivatized or underivatized, were heated at three different temperatures (60, 100, and 250 °C) at different exposure times (30 s, 60 s, and 300 s). All the samples were analyzed by liquid chromatography coupled to electrospray ionization mass spectrometry (LC/MS) and the data processed by XCMS Online (xcmsonline.scripps.edu). The results showed that heating at an elevated temperature of 100 °C had an appreciable effect on both the underivatized and derivatized molecules, and heating at 250 °C created substantial changes in the profile. For example, over 40% of the molecular peaks were altered in the plasma metabolite analysis after heating (250 °C, 300s) with a significant formation of degradation and transformation products. The analysis of 64 small molecule standards validated the temperature-induced changes observed on the plasma metabolites, where most of the small molecules degraded at elevated temperatures even after minimal exposure times (30 s). For example, tri- and diorganophosphates (e.g., adenosine triphosphate and adenosine diphosphate) were readily degraded into a mono-organophosphate (e.g., adenosine monophosphate) during heating. Nucleosides and nucleotides (e.g., inosine and inosine monophosphate) were also found to be transformed into purine derivatives (e.g., hypoxanthine). A newly formed transformation product, oleoyl ethyl amide, was identified in both the underivatized and derivatized forms of the plasma extracts and small molecule standard mixture, and was likely generated from oleic acid. Overall these analyses show that small molecules and metabolites undergo significant time-sensitive alterations when exposed to elevated temperatures, especially those conditions that mimic sample preparation and analysis in GC/MS experiments.