Simultaneous quantification of multiple endogenous biothiols in single living cells by plasmonic Raman probes

Fabrication of flexible SERS substrate based on Au nanostars and PDMS for sensitive detection of Thiram residue in apple juice

We developed a novel fabrication of flexible surface-enhanced Raman scattering (SERS) substrate to perform selective and sensitive determination of thiram residue in fruits and juices. Au nanostars (Au NSs) with multi-branching structure were self-assembled on aminated Polydimethylsiloxane (PDMS) slides by electrostatic interaction. By measuring the Thiram's characteristic peak intensity at 1371 cm^-1, the SERS method could distinguish Thiram from other pesticide residues. A good linear relationship between the peak intensity at 1371 cm^-1 and thiram's concentration was established at the range from 0.01 ppm to 100 ppm and the Limit of detection is 0.0048 ppm. We directly used this SERS substrate to detect Thiram in apple juice. By standard addition method, recoveries varied in the range of 97.05% to 106.00% and the RSD were from 3.26% to 9.35%. The SERS substrate exhibited a good sensitivity, stability and selectively for the detection of Thiram in food samples, which can be spread as a common method for the detection of pesticides in food samples.

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.

Heterometallic nanomaterials: Activity modulation, sensing, imaging and therapy

Heterometallic nanomaterials (HMNMs) display superior physicochemical properties and stability to monometallic counterparts, accompanied by wider applications in the fields of catalysis, sensing, imaging, and therapy due to synergistic effects between multi-metals in HMNMs. So far, most reviews have mainly concentrated on introduction of their preparation approaches, morphology control and applications in catalysis, assay of heavy metal ions, and antimicrobial activity. Therefore, it is very important to summarize the latest investigations of activity modulation of HMNMs and their recent applications in sensing, imaging and therapy. Taking the above into consideration, we briefly underline appealing chemical/physical properties of HMNMs chiefly tailored through the sizes, shapes, compositions, structures and surface modification. Then, we particularly emphasize their widespread applications in sensing of targets (e.g. metal ions, small molecules, proteins, nucleic acids, and cancer cells), imaging (frequently involving photoluminescence, fluorescence, Raman, electrochemiluminescence, magnetic resonance, X-ray computed tomography, photoacoustic imaging, etc.), and therapy (e.g. radiotherapy, chemotherapy, photothermal therapy, photodynamic therapy, and chemodynamic therapy). Finally, we present an outlook on their forthcoming directions. This timely review would be of great significance for attracting researchers from different disciplines in developing novel HMNMs.

Heterometallic nanomaterials display wide applications in the fields of catalysis, sensing, imaging and therapy due to synergistic effects between the multi-metals.

Simultaneous Quantification of Biothiols and Deciphering Diverse GSH Stability in Different Live Cells by 19F-Tag

GSH, Cys, Hcy, and H₂S are important biothiols and play important roles in the living systems. Quantitative and simultaneous determination of these biothiols under physiological conditions is still a challenge. Herein, we developed an effective ¹⁹F-reactive tag that readily interacts with these four biothiols for the generation of stable thioether products that have distinguishable ¹⁹F-chemical shifts. These thioester compounds encode the characteristic fingerprint profiles of each biothiols, allowing one to simultaneously quantify and determine these biothiols by 1D ¹⁹F NMR spectroscopy. The intra-/extracellular GSH in live cells was assessed by the established strategy, and remarkable variations in the GSH stability were determined between the normal mammalian cells and cancer cells. It is notable that GSH hydrolyzes efficiently in the out-membrane of the cancer cells and the lysates. In contrast, GSH remains stable in the tested normal cells.

A near-infrared fluorescence turn-on probe based on Michael addition-intramolecular cyclization for specific detection of cysteine and its applications in environmental water and milk samples and living cells

Owing to its important biological functions in many physiological and pathological processes, it is necessary to develop efficient and appropriate detection methods for monitoring the levels of Cys in biological systems. Based on this, a novel rhodol-isophorone derivative (RHI) was designed and synthesized as a reaction-based fluorescence probe for specific detection of Cys with high sensitivity and large Stokes shift (155 nm). This probe was composed of an acrylate moiety (recognition group) and a rhodol-isophorone derivative (fluorophore). Probe RHI could react with Cys rapidly (15 min) with a 100-fold fluorescence enhancement. The limit of detection value was calculated to be 0.168 μM. When Cys was added, the color of the probe RHI solution turned from yellow to blue, indicating that Cys could be monitored by the naked eye. In addition, probe RHI was successfully utilized for detecting Cys in environmental water and milk samples. More importantly, the probe could be applied to imaging Cys in living cells with low cytotoxicity and good biocompatibility.

Core-Shell Plasmonic Nanomaterials toward: Dual-Mode Imaging Analysis of Glutathione and Enhanced Chemodynamic Therapy

A simple process, rich information, and intelligent response are the goals pursued by cancer diagnosis and treatment. Herein, we developed a core-shell plasmonic nanomaterial (Au@MnO₂-DNA), which consisted of a AuNP core with an outer shell MnO₂ nanosheet decorated with fluorophore modified DNA, to achieve the aforementioned aims. On the basis of the unique optical properties of plasmonic nanoparticles and the oxidability of the shell MnO₂, scattering signal and fluorescence (FL) signal changes were both related to the expression level of glutathione (GSH), for which a dual-mode imaging analysis was successfully achieved on single optical microscope equipment with one-key switching. Meanwhile, the product of Mn²⁺ from the reaction between MnO₂ and GSH not only served as a smart chemodynamic agent to initiate Fenton-like reaction for achieving chemodynamic therapy (CDT) of cancer cells but also relieved the side effect of intracellular GSH in cancer therapy. Therefore, the core-shell plasmonic nanomaterials with dual modal switching features and diagnostic properties act as excellent probes for achieving bioanalysis of aberrant levels of intracellular GSH and simultaneously activating the CDT of cancer cells based on the in situ reactions in cancer cells.

A new lateral flow plasmonic biosensor based on gold-viral biomineralized nanozyme for on-site intracellular glutathione detection to evaluate drug-resistance level

Temozolomide (TMZ)-resistant glioblastoma multiforme (GBM) cells would have abnormal redox status due to bio-thiols, like glutathione (GSH), which constitute the most crucial defense system that protects cells from therapeutic agents. Current strategies for GSH detection often require sophisticated instruments that may not be available in laboratories with fewer resources. Here, we circumvent this problem by introducing a lateral flow plasmonic biosensor (LFPB) based on gold-viral biomineralized nanoclusters (AuVCs) as nanozymes that enables the detection of a few molecules with the naked eye and quantified by an auto-analysis software. The GSH level controls the growth of gold nanoparticles (AuNPs) and generates coloured patterns with distinct tonality, which are then auto-analyzed to calculate the GSH concentrations by smartphone with an auto-analysis software. Under the optimized conditions, grayscale value plotted against GSH concentration exhibited a linear relationship within the range of 25-500 μM with a limit of detection (LoD) of 9.80 μM and highly positive correlation between detected GSH level and TMZ drug-resistance level in GBM cells. This excellent property allowed our approach to be used for on-site determination of GSH levels in a rapid (i.e., within 30 min), simple (i.e., auto-analysis software), and cost-effective process (i.e., instrument-free) for cancer precision therapy.

NBD-based fluorescent probes for separate detection of cysteine and biothiols via different reactivities

A NBD-based fluorescent probe is developed to seperately detect Cys and all biothiols via different reactivity.

Direct Determination of Redox Statuses in Biological Thiols and Disulfides with Noncovalent Interactions of Poly(ionic liquid)s

The three most important redox couples, including cysteine (Cys)/cystine (Cyss), homocysteine (Hcys)/homocystine (Hcyss), and reduced glutathione (GSH)/glutathione disulfide (GSSG), are closely associated with human aging and many diseases. Thus, it is highly important to determine their redox statuses at the following two levels: (i) the redox identity in different thiols/disulfides and (ii) the redox ratio in a mixture of a specific couple. Herein, by using one single AIE-doped (AIE, aggregation-induced emission) photonic-structured poly(ionic liquid) (PIL) sphere as a virtual sensor array, we realize a direct determination of the redox status without a reducing pretreatment of disulfides, which will greatly promote the development of high-throughput and simple procedures. The pattern-recognition method uses the multiple noncovalent interactions of imidazolium-based PILs with these redox species to produce differential responses in both the photonic crystal and fluorescence dual channels. On the one hand, a single sphere enables the direct and simultaneous discrimination of the redox identities of Cys, Cyss, Hcys, Hcyss, GSH, and GSSG under the interference of other five commonly occurring thiols. On the other hand, this sphere also allows for not only a direct quantification of the GSH/GSSG ratios without previously determining the individual concentrations of GSH and GSSG but also the accurate prediction of the ratios in unknown redox samples. To further demonstrate applications of this method, redox mixtures in a biological sample are differentiated. Additionally, quantum calculations further support our assignments for interactions between the imidazolium-based PILs and these redox species.

Microbial Redox Regulator-Enabled Pulldown for Rapid Analysis of Plasma Low-Molecular-Weight Biothiols

Although low-molecular-weight (LMW) biothiols function as a disease indicator in plasma, rapidly and effectively analyzing them remains challenging in the extracellular oxidative environment due to technical difficulties. Here, we report a newly designed, affinity pulldown platform using a Bacillus subtilis-derived organic hydroperoxide resistance regulatory (OhrR_BS) protein and its operator dsDNA for rapid and cost-effective analyses of plasma LMW biothiols. In the presence of organic hydroperoxide, LMW biothiols triggered the rapid dissociation of FAM-labeled dsDNA from FLAG-tagged OhrR_BS via S-thiolation of OhrR_BS on anti-FLAG antibody-coated beads, which led to a strong increase of fluorescence intensity in the supernatant after pulldown. This method was easily extended by using a reducing agent to detect free and total LMW biothiols simultaneously in mouse plasma. Unlike free plasma LMW biothiols, total plasma LMW biothiols were more elevated in ΔLDLR mice than those in normal mice. Owing to the rapid dissociation of OhrR/dsDNA complexes in response to LMW biothiols, this pulldown platform is immediately suitable for monitoring rapid redox changes in plasma LMW biothiols as well as studying oxidative stress and diseases in blood.

An ultralow concentration of two-photon fluorescent probe for rapid and selective detection of lysosomal cysteine in living cells

Herein we reported a two-photon (TP) fluorescence "turn-on" probe MNPO, exhibiting high selectivity and sensitivity towards intracellular cysteine (Cys) with excellent lysosomal localization. The probe displayed fast response towards Cys over homocysteine (Hcy), glutathione (GSH), and other various analytes under physiological conditions. Low cytotoxicity made it successful for TP imaging of Cys in HeLa cells with an ultralow probe concentration of 250 nM, and a rapid response of only 10 min. Simultaneously, colocalization experiments in lysosome demonstrated its ability for specific in situ detection of lysosomal Cys in living cells, which shed light on its potential applications in biomedical applications. Beyond that MNPO was successfully applied for TP imaging of Cys in mice organ tissues such as heart, liver, and spleen, and the penetration depth of mice heart tissue was up to 184 μm, which disclosed the predominant TP characteristic. We believe that this study will provide some useful information toward diagnosis and treatment of pathogenesis associated with Cys or lysosomes in future.

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.

Monitoring the Changes of pH in Lysosomes during Autophagy and Apoptosis by Plasmon Enhanced Raman Imaging

Lysosomes are acidic organelles that not only participate in intracellular degradation but also relate to various cellular functions. Abnormal pH in lysosomes would lead to lysosomal dysfunction, which may further result in many diseases. In this work, we statistically analyze the pH change in the lysosomes of HeLa cells model by using surface enhanced Raman scattering (SERS) imaging technique. We prepared a plasmon Raman pH probe and localized the pH probe to lysosomes via an incubation-depletion method. The pH profiles within lysosomes during the process of cellular autophagy and apoptosis were monitored in situ by SERS imaging. The pH in lysosomes decreased slightly during the process of autophagy, while the pH in lysosomes increased during apoptosis. The phenomenon, in general, is consistent with our current biological knowledge. However, we did not observe significant variation of pH between different individual cells. This information might provide an in depth understanding about the relationship of lysosomal pH with fundamental cellular functions and mechanism of diseases.

Label-free gold nanorods sensor array for colorimetric detection and discrimination of biothiols in human urine samples

Biothiols play important roles in regulating redox balance in biological systems, but their discrimination is challengeable. In this work, a colorimetric nanosensing array for biothiols was established, which was composed of gold nanorods (AuNRs) and metal ions (Hg²⁺, Pb²⁺, Cu²⁺, Ag⁺). By employing label-free AuNRs as the colorimetric probe, and the color and spectral changes of AuNRs as the output signal, principal component analysis (PCA) was applied to processing the signal and generating a clustering map. Due to the different binding affinity between biothiols and metal ions, AuNRs exhibited a unique pattern to form a fingerprint-like colorimetric array, which was able to discriminate five biothiols by the naked eyes. This strategy combines PCA and sensor array to achieve rapid and accurate discrimination and detection of biothiols. In addition, the method shows the great potential in analysis of biothiols in human urine samples.

Sensitive analysis of multiple low-molecular-weight thiols in a single human cervical cancer cell by chemical derivatization-liquid chromatography-mass spectrometry

Simultaneous quantification of multiple low-molecular-weight thiols from a single HeLa cell was realized by chemical derivatization assisted LC-MS method.

A high precision MUA-spaced single-cell sensor for cellular receptor assay based on bifunctional Au@Cu-PbCQD nanoprobes

A single-cell sensor with a spatial architecture was firstly fabricated for realizing high precision single-cell analysis using an 11-mercaptoundecanoic acid (MUA)-spaced sensing interface to prop up single cells and provide a suitable space for effective nanoprobe labeling. Mercapto acids (MA) with different carbon chain lengths were optimized and MUA was selected to provide optimal interspace on the electrodeposited PANI/AuNP substrates, and its carboxyl could couple with folic acid to capture cancer cells. Bifunctional Au@Cu-PbCQD nanoprobes, in which the AuNP cores were linked with lead-coadsorbed carbon quantum dots (PbCQDs) by a copper(ii) ion bridge, were firstly synthesized and applied as highly sensitive electrochemiluminescence (ECL) probes and electrochemical probes. Hyaluronic acid (HA)-functionalized Au@Cu-PbCQD nanoprobes were labelled on MCF-7 cells via specific recognition to the CD44 receptor, which served as the research model. The ECL response of the sensor was applied to evaluate the validity of nanoprobe labeling. With MUA modified, the sensor was able to enhance the ECL intensity by 37.5 ± 3.9%, indicating the remarkable amelioration of the accuracy of single-cell analysis. To take advantage of the bifunctional nanoprobes, differential pulse voltammetry (DPV) was further applied to confirm the feasibility of the proposed single-cell sensor with a spatial architecture. Therefore, the novel strategy provides a single-cell analysis platform to acquire high-precision analytical results, and more accurately to elucidate cellular heterogeneity and biological function.

Inverse Opal Photonic Crystals as an Optofluidic Platform for Fast Analysis of Hydrocarbon Mixtures

Most of the reported optofluidic devices analyze liquid by measuring its refractive index. Recently, the wettability of liquid on various substrates has also been used as a key sensing parameter in optofluidic sensors. However, the above-mentioned techniques face challenges in the analysis of the relative concentration of components in an alkane hydrocarbon mixture, as both refractive indices and wettabilities of alkane hydrocarbons are very close. Here, we propose to apply volatility of liquid as the key sensing parameter, correlate it to the optical property of liquid inside inverse opal photonic crystals, and construct powerful optofluidic sensors for alkane hydrocarbon identification and analysis. We have demonstrated that via evaporation of hydrocarbons inside the periodic structure of inverse opal photonic crystals and observation of their reflection spectra, an inverse opal film could be used as a fast-response optofluidic sensor to accurately differentiate pure hydrocarbon liquids and relative concentrations of their binary and ternary mixtures in tens of seconds. In these 3D photonic crystals, pure chemicals with different volatilities would have different evaporation rates and can be easily identified via the total drying time. For multicomponent mixtures, the same strategy is applied to determine the relative concentration of each component simply by measuring drying time under different temperatures. Using this optofluidic sensing platform, we have determined the relative concentrations of ternary hydrocarbon mixtures with the difference of only one carbon between alkane hydrocarbons, which is a big step toward detailed hydrocarbon analysis for practical use.

Hydroxyapatite nanoparticle based fluorometric determination and imaging of cysteine and homocysteine in living cells

Fluorescent hydroxyapatite nanoparticles (HAP-NPs) were prepared by reacting calcium ion with phosphate in the presence of Eu(III) ion. The HAP-NPs display large Stokes' shift and two strong fluorescence emissions with peaks at 590 nm and 615 nm when excited at 250 nm. The HAP-NPs also have good photostability and water solubility. The HAP-NPs combined with Cu(II) were applied to fluorometric determination of cysteine and homocysteine in biological samples and in living cells. In this detection scheme, the fluorescence of HAP-NPs is initially quenched by Cu(II). The addition of biothiols results in the formation of Cu(II)-thiol complexes and leads to fluorescence recovery. The assay allows cysteine to be detected with a 110 nM detection limit, and homocysteine with a 160 nM detection limit. The assay was successfully applied to the analysis of cysteine in spiked human serum samples and to imaging of cysteine in HeLa cells, and this demonstrates its potential for clinical testing and in biomedical research. Graphical abstract Fluorescent hydroxyapatite nanoparticles were synthesized and combined with Cu²⁺ for fluorescence sensing of biothiols (cysteine and homocysteine) in complex biological samples and in living cells.