Fabrication of a "Selenium Signature" Chemical Probe-Modified Paper Substrate for Simultaneous and Efficient Determination of Biothiols by Paper Spray Mass Spectrometry

In Situ Single Au@Cu2O Core-Shell Nanoparticle Analysis-Enhanced Ultrasensitive Detection of Biothiols Using Light Scattering Imaging

Dark-field microscopy (DFM) as a single particle analysis (SPA) technique has been developed rapidly in recent years because of its high signal-to-noise ratio, enhanced sensitivity, and sufficient spatial and temporal resolution. Here, an in situ single Au@Cu2O core-shell nanoparticle (Au@Cu2O NP) light scattering imaging analysis was reported to realize the ultrasensitive detection of biothiols-cysteine (Cys) and glutathione (GSH). Based on the specific binding of Cu(I) with -SH to the formation of the Cu-S bond, it triggered the decomposition of the Cu2O shell and exposure of the Au nanorods (Au NRs) in the presence of biothiols. Moreover, the process of Cu2O shell dissolution has been observed in real time under DFM, which indicated that the scattering color changed from bright green to dark red and the scattering intensity decreased, correspondingly. Compared with ex situ SPA, in situ SPA exhibited significantly high sensitivity due to the effect of concentration polarization, which exhibited linear correlations over broad concentration ranges (Cys: 0.05-3 nM, GSH: 0.1-10 nM), with low detection limits of 15.52 pM (Cys) and 75.07 pM (GSH). Therefore, this work provides a smart strategy to find promising applications for the ultrasensitive detection of biomolecules through SPA.

Iridium Isotope Tag-Assisted LC-MS Method for Global Profiling and Quantification of Nonvolatile Serum Fatty Acids in Nonalcoholic Fatty Liver Mice

Highly accurate and sensitive measurements of fatty acids (FAs) in biological samples are essential for advancing our understanding of their diverse biofunctions. In this work, based on the characteristic isotope pattern of iridium (191/193Ir), we employed an iridium-encoded amine (Ir-NH2) as the derivatization reagent to establish a selective and sensitive liquid chromatography-mass spectrometry (LC-MS) method for rapid identification and accurate quantification of FAs in biological samples. Upon derivatization, nonvolatile FAs were transformed into amide derivatives tagged with a charged iridium tag, exhibiting improved sensitivity and selectivity in the electrospray ionization (ESI) positive ion mode. By leveraging the unique 2.002 Da mass shift and the 3:5 peak intensity ratio from the natural 191Ir and 193Ir isotopes, we can rapidly and efficiently screen the potential carboxyl-containing metabolites from biological samples. Compared to other existing methods, our technique offers higher sensitivity, better signal-to-noise ratio, lower detection limit (1.2-8.4 pg/mL), and easier quantification due to the clear identification of iridium-tagged derivatives. With this method, a total of 58 FAs, including both saturated and unsaturated types, were detected in mice serum lipid extracts, with carbon chain lengths varying from C9 to C24. More importantly, this method was successfully employed for global profiling of nonvolatile serum FAs from mice with nonalcoholic fatty liver disease (NAFLD), providing a novel means for detecting them and offering new avenues for exploring their functional roles and disease associations.

PyDNA-templated AgNPs coupled with poly (β‑cyclodextrin) enhanced fluorescence: A facile platform for signal amplification detection of biothiols in living cells and zebrafish

Accurate and sensitive fluorescence imaging of biothiols is essential for understanding the mechanism underlying some physiological and pathological events, as well as the prevention and diagnosis of diseases. However, low signal transduction efficiency and poor biocompatibility of fluorescence tags associated with current sensors hinder their potential utilizations. Herein, a smart biothiols sensitive vivo imaging platform on the basis of amplifying nanoprobe has been designed. The as-prepared nanoprobe are composed of 5'-pyrene-labeled single-stranded DNA with C-rich (PyDNA), DNA-templated silver nanoparticles (AgNPs) and amplification carrier β-cyclodextrin-based polymer (βCDP). PyDNA was not only used as a signal tag, but also as a templated DNA for in situ growth of silver nanoparticles (PyDNA-AgNPs), resulting in fluorescence quenching of PyDNA through FRET. In the presence of GSH as a model biothiol, replace PyDNA off from the surface of AgNPs owing to the interact intensely between biothiol and AgNPs by forming S-Ag bonds, resulting in a fluorescence enhancement. Simultaneously, the released PyDNA was able to form a host-guest inclusion complex with βCDP to achieve signal amplification (10.1-fold enhancement). The obtained nanoprobe exhibits high sensitivity and selectivity to glutathione (GSH) with a detection limit as low as 71 nM. Using HeLa cells as a model, this nanoprobe not only realizes the highly sensitive amplifying detection and imaging of GSH in living cells, but also applies in vivo monitoring of exogenous GSH level in zebrafish. Further use of probes to reveal the overexpression of GSH with the high-contrast imaging in the tumor tissues from the lung disease model mice and clinical lung cancer patients was successfully demonstrated. It provides a facile tool for highly sensitive biothiols imaging and may pave a new avenue for the early and accurate diagnosis of tumors.

One-component dual-mode sensor array for identification and quantification of biothiols

Biothiol analysis is significant to health assessment and early detection of potential diseases. Considering practical requirements, simple and rapid identification and determination of biothiols are still a great challenge due to the similar structures. Fortunately, the recently emerging colorimetric sensor array technique makes such a task possible. Herein, one-component dual-mode sensor array consisting of carbon dots (CDs) and Ag nanoparticles (AgNPs) system was designed for identification and quantification of biothiols. The identification principle is based on the inner filter effect (IFE) and different binding constants. Due to the IFE between CDs and AgNPs, the fluorescence of CDs was quenched, but recovered again after addition of biothiols because of the binding of biothiols with AgNPs. Significantly, the fluorescence recovered in varying degree due to the different binding constants of biothiols to AgNPs. Meanwhile, the absorbance of the system decreased and the color of the solution deepened. Therefore, the CDs-AgNPs system with fluorescence and absorbance response was used as the single sensing unit and generated the cross-responsive signal for different biothiols. The sensor array achieved 100 % accuracy in identifying biothiols and biothiol mixtures. Moreover, the rapid quantification of biothiols in serum samples was also achieved by RGB-based smartphone colorimetry. The way to construct one component sensor array with dual mode signal outputs tremendously saves cost and time, providing a powerful tool for the identification of different biothiols. In addition, the rapid quantification of biothiols in serum samples based on RGB-based smartphone colorimetry demonstrated its powerful application prospects in disease diagnosis.

Dyes-encapsulated metal-organic cage as fluorescence sensor array for the auxiliary differential diagnosis of MCD and FSGS in early renal disorders

Both minimal change disease (MCD) and focal segmental glomerular sclerosis (FSGS) are the pathological types of primary nephrotic syndrome (PNS) and cannot be readily distinguished owing to their highly similar clinical presentations. Currently, methods for clinical MCD and FSGS diagnosis still rely on invasive renal biopsy which impede rapid and accurate diagnosis for timely treatment management. In this study, a novel diagnostic strategy by introducing the dyes with spironolactone structure into the metal-organic cage to construct three dye@MOCs composites has been developed and employed as fluorescence sensor array for assisting in the auxiliary differential diagnosis of MCD and FSGS based on the distinguishable biothiols in urine. Through the statistical analysis technique for the interpretation of response patterns, the weak fluorescent of dye@MOCs sensor array exhibited unique patterns of fluorescence enhancement when biothiols appeared, forming the unique "off-on" sensor array. Additionally, dye@MOCs sensor array exhibited excellent selectivity and good stability, indicating their potentially actual applications. Outstandingly, as an important example, it was demonstrated for the first time that dye@MOCs sensor array can be applied to the auxiliary differential diagnosis of MCD and FSGS patients based on the differentiable biothiols level in urine using non-invasively methods, potentially avoiding invasive renal biopsy diagnosis and overcoming the limitations of conventional urine examinations, illustrating its potential applications in the auxiliary differential diagnosis and research of related diseases in the forthcoming era. And moreover, this opens new avenues for reliable disease auxiliary diagnosis and differentiation, setting a new benchmark for accuracy and reliability in medical assessments.

Simultaneous Quantification of Carboxylate Enantiomers in Multiple Human Matrices with the Hydrazide-Assisted Ultrahigh-Performance Liquid Chromatography Coupled with Tandem Mass Spectrometry

Many chiral carboxylic acids with α-amino, α-hydroxyl, and α-methyl groups are concurrently present in mammals establishing unique molecular phenotypes and multiple biological functions, especially host-microbiota symbiotic interactions. Their chirality-resolved simultaneous quantification is essential to reveal the biochemical details of physiology and pathophysiology, though challenging with their low abundances in some biological matrices and difficulty in enantiomer resolution. Here, we developed a method of the chirality-resolved metabolomics with sensitivity-enhanced quantitation via probe-promotion (Met-SeqPro) for analyzing these chiral carboxylic acids. We designed and synthesized a hydrazide-based novel chiral probe, (S)-benzoyl-proline-hydrazide (SBPH), to convert carboxylic acids into amide diastereomers to enhance their retention and chiral resolution on common C18 columns. Using the d5-SBPH-labeled enantiomers as internal standards, we then developed an optimized ultrahigh-performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS) method for simultaneous quantification of 60 enantiomers of 30 chiral carboxylic acids in one run. This enantiomer-resolved method showed excellent sensitivity (LOD < 4 fmol-on-column), linearity (R2 > 0.992), precision (CV < 15%), accuracy (|RE| < 20%), and recovery (80-120%) in multiple biological matrices. With the method, we then quantified 60 chiral carboxylic acids in human urine, plasma, feces, and A549 cells to define their metabolomic phenotypes. This provides basic data for human phenomics and a promising tool for investigating the mammal-microbiome symbiotic interactions.

Tentative identification of phytochelatins, their derivatives, and Cd-phytochelatin complexes in Ocimum basilicum L. roots by Paper Spray Mass Spectrometry

An unprecedented and direct PS-MS (paper spray ionization mass spectrometry) method was proposed for the detection of native peptides, that is, glutathiones (GSHs), homoglutathiones (hGSHs), and phytochelatins (PCs), in basil (Ocimum basilicum L.) roots before and after cadmium exposure. The roots were submitted to cold maceration followed by sonication with formic acid as the extractor solvent for sample preparation. PS-MS was used to analyze such extracts in the positive mode, and the results allowed for the detection of several GSHs, hGSHs, and PCs. Some of these PCs were not distinguished in the control samples, that is, basil roots not exposed to cadmium. Other PCs were noticed in both types of roots, uncontaminated and cadmium-contaminated, but the intensities were higher in the former samples. Moreover, long-time exposure to cadmium stimulated the formation of some of these PCs and their cadmium complexes. The results, therefore, provided some crucial insights into the defense mechanism of plants against an external stress condition due to exposure to a toxic heavy metal. The present study represents a promising alternative to investigate other crucial physiological processes in plants submitted to assorted stress conditions.

Identification of sulfhydryl-containing proteins and further evaluation of the selenium-tagged redox homeostasis-regulating proteins

Chemoproteomic profiling of sulfhydryl-containing proteins has consistently been an attractive research hotspot. However, there remains a dearth of probes that are specifically designed for sulfhydryl-containing proteins, possessing sufficient reactivity, specificity, distinctive isotopic signature, as well as efficient labeling and evaluation capabilities for proteins implicated in the regulation of redox homeostasis. Here, the specific selenium-containing probes (Se-probes) in this work displayed high specificity and reactivity toward cysteine thiols on small molecules, peptides and purified proteins and showed very good competitive effect of proteins labeling in gel-ABPP. We identified more than 6000 candidate proteins. In TOP-ABPP, we investigated the peptide labeled by Se-probes, which revealed a distinct isotopic envelope pattern of selenium in both the primary and secondary mass spectra. This unique pattern can provide compelling evidence for identifying redox regulatory proteins and other target peptides. Furthermore, our examiation of post-translational modification (PTMs) of the cysteine site residues showed that oxidation PTMs was predominantly observed. We anticipate that Se-probes will enable broader and deeper proteome-wide profiling of sulfhydryl-containing proteins, provide an ideal tool for focusing on proteins that regulate redox homeostasis and advance the development of innovative selenium-based pharmaceuticals.

Simultaneous Detection of Aldehyde Metabolites by Light-Assisted Ambient Ionization Mass Spectrometry

In the clinic, small-molecule metabolites (SMMs) in blood are highly convincing indicators for disease diagnosis, such as cancer. However, challenges still exist for detection of SMMs due to their low concentration and complicated components in blood. In this work, we report the design of a novel "selenium signature" nanoprobe (Se nanoprobe) for efficient identification of multiple aldehyde metabolites in blood. This Se nanoprobe consists of magnetic nanoparticles that can enrich aldehyde metabolites from a complex environment, functionalized with photosensitive "selenium signature" hydrazide molecules that can react with aldehyde metabolites. Upon irradiation with UV, the aldehyde derivatives can be released from the Se nanoprobe and further sprayed by mass spectrometry through ambient ionization (AIMS). By quantifying the selenium isotope distribution (MS/MS) from the derivatization product, accurate detection of several aldehyde metabolites, including valeraldehyde (Val), heptaldehyde (Hep), 2-furaldehyde (2-Fur), 10-undecenal aldehyde (10-Und), and benzaldehyde (Ben), is realized. This strategy reveals a new solution for quick and accurate cancer diagnosis in the clinic.

Rapid fabrication of hydrophobic/hydrophilic patterns on paper substrates for paper spray mass spectrometry

A simple, rapid chemical coating and patterning method was developed and optimized for paper-based substrates for use in paper spray mass spectrometry (PS-MS). A variety of chlorosilanes were explored for coating paper substrates, and their effectiveness in forming hydrophobic surfaces was characterized via contact angle goniometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Trichloromethylsilane was selected as the primary coating agent because of the short time required to produce a hydrophobic surface (contact angle > 130°), as well as the ease of patterning. Patterning was performed using 3D-printed masks and an oxygen/plasma cleaner. Optimal mask thickness and oxygen/plasma cleaning parameters were determined to produce channels varying from 0.5 to 2.5 mm in width. The effectiveness of the patterned substrates for PS-MS was determined via analysis of four antiretrovirals: emtricitabine, lamivudine, efavirenz, and dolutegravir. Calibration curves were made for each antiretroviral at varying channel widths, and the limits of detection and limits of quantification for each drug were determined. These results show that this patterning method results in an average 7.2-fold improvement in sensitivity and an average 190-fold improvement in limits of detection over uncoated paper substrates in a neat matrix. In a proof-of-concept experiment, calibration curves were generated for each antiretroviral in urine. A patterned paper substrate with a 2-mm channel resulted in an average 7.4-fold improvement in sensitivity and an average 18-fold improvement in limits of detection over uncoated paper substrates.

Applications of ambient ionization mass spectrometry in 2021: An annual review

Ambient ionization mass spectrometry (AIMS) has revolutionized the field of analytical chemistry, enabling the rapid, direct analysis of samples in their native state. Since the inception of AIMS almost 20 years ago, the analytical community has driven the further development of this suite of techniques, motivated by the plentiful advantages offered in addition to traditional mass spectrometry. Workflows can be simplified through the elimination of sample preparation, analysis times can be significantly reduced and analysis remote from the traditional laboratory space has become a real possibility. As such, the interest in AIMS has rapidly spread through analytical communities worldwide, and AIMS techniques are increasingly being integrated with standard laboratory operations. This annual review covers applications of AIMS techniques throughout 2021, with a specific focus on AIMS applications in a number of key fields of research including disease diagnostics, forensics and security, food safety testing and environmental sciences. While some new techniques are introduced, the focus in AIMS research is increasingly shifting from the development of novel techniques toward efforts to improve existing AIMS techniques, particularly in terms of reproducibility, quantification and ease-of-use.

Colorimetric determination of biothiols with AuNPs@MoS2 NSs as a peroxidase mimetic enzyme

The synthesis of AuNPs@MoS2 NSs was achieved and the sensing of biothiols was carried out using AuNPs@MoS2 NSs as enzyme mimics.

Synergistic Combination of Facile Thiol-Maleimide Derivatization and Supramolecular Solvent-Based Microextraction for UHPLC-HRMS Analysis of Glutathione in Biofluids

Glutathione (GSH) is the most abundant non-protein thiol in biofluids, enabling diverse physiological functions. Among the proposed methods for GSH detection, ultra-high-performance liquid chromatography (UHPLC) coupled with high-resolution mass spectrometry (HRMS) has the advantages of high sensitivity and efficiency. In this study, a novel analytical method was developed for the determination of GSH using supramolecular solvent (SUPRAS)-based dispersive liquid–liquid microextraction (DLLME) and UHPLC–HRMS. N-Laurylmaleimide was dissolved in tetrahydrofuran, which served three functions: 1) precipitate the proteins present in the biofluid sample, 2) provide a reaction environment for derivatization, and 3) enable the use of SUPRAS as the dispersing agent. Critical parameters were optimized based on single factor testing and response surface methodology. The established method was validated in terms of linearity, accuracy, precision, and successful quantitative analysis of GSH in saliva, urine, and plasma samples. Experimental results showed that SUPRAS as an extraction solvent was particularly suitable for the extraction of GSH from complex matrices. The current study provides a useful tool for accurate measurements of GSH concentrations, which could potentially be used for clinical diagnostics.

Turning waste into treasure: chicken eggshell membrane derived fluorescent carbon nanodots for the rapid and sensitive detection of Hg2+ and glutathione

Herein, a green, economical, and waste-utilization approach is reported for the synthesis of water-soluble carbon nanodots (C-Dots) with a high fluorescence quantum yield of 19.5%. As a common protein-rich waste, eggshell membrane was selected as a cost-effective and ideal precursor to prepare C-Dots using the microwave method. The as-prepared C-Dots showed a maximum emission at 375 nm with an excitation wavelength at 235 nm. The fluorescent C-Dots were adopted as a sensitive probe for the rapid detection of Hg²⁺ and glutathione (GSH) based on the fluorescence off and on (turn-off-on) strategy. This was ascribed to the fact that Hg²⁺ could effectively quench the fluorescence of the C-Dots and GSH was able to prevent fluorescence quenching owing to the specific binding between Hg²⁺ and GSH. The designed method exhibited a high sensitivity and selectivity towards the detection of Hg²⁺ and GSH. Under the optimized conditions, the method showed a good linear relationship with Hg²⁺ concentration in the range from 100 nM to 50 μM with a detection limit of 32.0 nM. For GSH detection, it displayed a linear range from 50 nM to 10 μM with a detection limit of 9.8 nM. Moreover, this method was successfully applied to detect GSH in human serum samples. The eggshell derived fluorescent C-Dots pave the way for economical environmental and biological analyses.