Electrochemical Molecular Switch for the Selective Profiling of Cysteine in Live Cells and Whole Blood and for the Quantification of Aminoacylase-1

Near-Infrared Fluorescent Probe for the Detection of Cysteine

Hemicyanine dyes are an ideal structure for building near-infrared fluorescent probes due to their excellent emission wavelength properties and biocompatibility in biological imaging field. Developing a near-infrared fluorescent probe capable of detecting cysteine (Cys) was the aim of this study. A novel developed fluorescent probe P showed high selectivity and sensitivity to Cys in the presence of various analytes. The detection limit of P was found to be 0.329 μM. The MTT assay showed that the probe was essentially non-cytotoxic. Furthermore, the probe was successfully used as cysteine imaging in living cells and mice.

Self-Immolative Electrochemical Redox Substrates: Emerging Artificial Receptors in Sensing and Biosensing

The development of artificial receptors has great significance in measurement science and technology. The need for a robust version of natural receptors is getting increased attention because the cost of natural receptors is still high along with storage difficulties. Aptamers, imprinted polymers, and nanozymes are some of the matured artificial receptors in analytical chemistry. Recently, a new direction has been discovered by organic chemists, who can synthesize robust, activity-based, self-immolative organic molecules that have artificial receptor properties for the targeted analytes. Specifically designed trigger moieties implant selectivity and sensitivity. These latent electrochemical redox substrates are highly stable, mass-producible, inexpensive, and eco-friendly. Combining redox substrates with the merits of electrochemical techniques is a good opportunity to establish a new direction in artificial receptors. This Review provides an overview of electrochemical redox substrate design, anatomy, benefits, and biosensing potential. A proper understanding of molecular design can lead to the development of a library of novel self-immolative redox molecules that would have huge implications for measurement science and technology.

Development of an activity-based ratiometric electrochemical probe of the tumor biomarker γ-glutamyl transpeptidase: Rapid and convenient sensing in whole blood, urine and live-cell samples

γ-Glutamyl transpeptidase (GGT) is a key biomarker for cancer diagnosis and post-treatment surveillance. Currently available methods for sensing GGT show high potential, but face certain challenges including an inability to be used to directly sense analytes in turbid biofluid samples such as whole blood without tedious sample pretreatment. To overcome this issue, activity-based electrochemical probes (GTLP and GTLPOH) were herein developed for a convenient and specific direct targeting of GGT activity in turbid biosamples. Both probes were designed to have GGT catalyze the hydrolysis of the gamma-glutamyl amide moiety of the probe, and result in a self-immolative reaction and concomitant ejection of the masked amino ferrocene reporter. The GTLPOH probe, delivered distinctive key results including high sensitivity, high affinity, a wide detection range of 2-100 U/L, and low LOD of 0.38 U/L against GGT. This probe delivered a precise target for sensing GGT and was free of interference from other electroactive biological species. Furthermore, the GTLPOH probe was employed to monitor and quantify the activity of GGT on the surfaces of tumor cells. The designed sensing method was also validated by the direct quantitative measurement of GGT activity in whole blood and urine samples, and the results were found to be consistent with those of the standard fluorometric assay kit. Thus, GTLPOH is of great significance for its promise as a point-of-care tool for early-stage cancer diagnosis as well as a new drug screening method.

Aggregation-caused dual-signal response of gold nanoclusters for ratiometric optical detection of cysteine

Designing ratiometric sensors for cysteine (Cys) monitoring with high accuracy is of great significance for disease diagnosis and biomedical studies. The current ratiometric methods mainly rely on multiplex probes, which not only complicates the operation but also increases the cost, making it difficult for quantitative Cys detection in resource-limited areas. Herein, one-pot prepared gold nanoclusters (Au NCs) that glow red fluorescent were synthesized by employing glutathione as the stabilizer and reducing agent. When Fe3+ is present with Au NCs, the fluorescence is quenched and the scattering is strong because of the aggregation of Au NCs. With introduction of Cys, Cys can efficiently compete with glutathione-modified Au NCs for Fe3+, which leads to increase of fluorescence and decrease of scattering. The ratiometric determination of Cys can be thereby realized by collecting the fluorescence and SRS spectrum simultaneously. The linear range for Cys was 5-30 µM with a detection limit of 1.5 µM. In addition, the sensing system exhibits good selectivity for Cys and shows potential application in biological samples.

ACY1 Downregulation Enhances the Radiosensitivity of Cetuximab-Resistant Colorectal Cancer by Inactivating the Wnt/β-Catenin Signaling Pathway

Treatment of cetuximab-resistant colorectal cancer (CRC) is a global healthcare problem. This study aimed to assess the effects of radiotherapy on cetuximab-resistant CRC and explore the underlying mechanism. We established a cetuximab-resistant HCT116 cell line (HCT116-R) by extracorporeal shock. Differentially expressed mRNAs were screened from cells treated with different radiation doses using second-generation high-throughput sequencing. Sequence data showed that ACY1 was significantly downregulated in HCT116-R cells after irradiation. Analysis of the GEO and TCGA datasets revealed that high ACY1 expression was associated with lymph node metastasis and a poor prognosis in CRC patients. In addition, immunohistochemistry results from CRC patients revealed that ACY1 protein expression was related to cetuximab resistance and lymph node metastasis. These findings suggested that ACY1 may function as an oncogene to promote CRC progression and regulate the radiosensitivity of cetuximab-resistant CRC. As expected, ACY1 silencing weakened the proliferation, migration, and invasion abilities of HCT116-R cells after radiotherapy. Mechanistically, TCGA data demonstrated that ACY1 expression was closely related to the Wnt/β-catenin pathway in CRC. We validated that radiotherapy first reduced β-catenin levels, followed by decreased expression of the metastasis-related protein E-cadherin. Silencing ACY1 dramatically enhanced these changes in β-catenin and E-cadherin after radiotherapy. In conclusion, ACY1 downregulation could enhance the radiosensitivity of cetuximab-resistant CRC by inactivating Wnt/β-catenin signaling, implying that ACY1 may serve as a radiotherapy target for cetuximab-resistant CRC.

A gold-silver bimetallic nanocluster-based fluorescent probe for cysteine detection in milk and apple

Noble metal nanoclusters have attracted much attention due to their excellent optical properties. In the present work, a silver-doped gold-based bimetallic nanoclusters (Au/Ag NCs) were reasonably designed and prepared through a one-pot method by using 5-mercapto-1-tetrazolea-acetic acid sodium salt (MTAS) as a protector and capping agent. In comparison with the monometallic nanoclusters, Ag-doped metallic nanoclusters show better performance. The particle size of the MTAS-Au/Ag NCs is slightly larger than that of the undoped Au NCs by about 1.86 ± 0.5 nm, and the MTAS-Au/Ag NCs exhibit an emission peak at 635 nm with a quantum yield (QY) of 3.05%. The presence of cysteine (Cys) induces efficient quenching of the photoluminescence of the obtained Au/Ag NCs, achieving the sensitive detection of Cys with a detection limit of 16 nM. The fluorescence quenching rate of the nano fluorescent probe has a linear relationship with the cysteine concentration. Under the best detection conditions, the linear range for Cys detection with MTAS-Au/Ag NCs as a probe is 0.05-25.0 μM. Moreover, this probe has been successfully applied to the analysis of Cys in milk and apples, and a satisfactory recovery rate has been obtained, indicating the effectiveness and reliability of the sensor system for the detection of actual samples.

A NIR fluorescence probe for monitoring Cys upregulation induced by balsam pear polysaccharide and imaging in zebrafish

In this work, we introduced the acrylate recognition group into dicyanoisophorone derivative DCI-C-OH to construct the NIR fluorescent probe DCI-C-Cys with a large Stokes shift (240 nm). DCI-C-Cys could specifically respond to Cys, resulting in a 22-fold increase in fluorescence intensity at 702 nm. Meanwhile, the probe has the advantages of good water solubility, high sensitivity (93 nM), and excellent biocompatibility. Moreover, DCI-C-Cys successfully monitored endogenous and exogenous Cys in HepG2 cells and zebrafish. Most importantly, we found that balsam pear polysaccharide could lead to the increase of intracellular Cys levels, which might be conducive to the further study of the antioxidant mechanism of balsam pear polysaccharide.

Convenient and ultrasensitive detection of live Salmonella using ratiometric electrochemical molecular substrates

Salmonella contamination is a major concern in food and public health safety, and carrying out episodic monitoring of Salmonella contamination in food and water bodies is essential for safeguarding public health and the economy. Therefore, there is an urgent need to develop an easy-to-operate Salmonella-targeting point-of-care detection platform. To this end, we designed two activity-based latent ratiometric electrochemical molecular substrates, denoted as Sal-CAF and Sal-NBAF, specifically for achieving easy, rapid, and selective profiling of Salmonella esterase (a Salmonella biomarker) under physiological conditions. The octyl esters of the substrates were cleaved by the esterase and triggered the trimethyl lock to eject the electron-rich aminoferrocene derivatives (CAF and NBAF), and the corresponding electrochemical signals were tracked at the negative region (-0.08 V vs Ag/AgCl) of the voltammetric spectrum. The Sal-CAF substrate was used to determine the concentration of Salmonella in a wide dynamic range (1.03 × 10⁵-1.1 × 10¹⁰ CFU mL^-1) with a low detection limit of 39.27 × 10³ CFU mL^-1. The developed probes were tested against various bacteria but were only activated by live Salmonella. Furthermore, the Sal-CAF probe was used directly in quantifying spiked live Salmonella spiked in milk samples and also used to effectively monitor and quantify Salmonella production in real-time. These achievements indicated the Sal-CAF probe to be a promising platform for point-of-care Salmonella analysis.

Michael addition–elimination–cyclization based turn-on fluorescence (MADELCY TOF) probes for cellular cysteine imaging and estimation of blood serum cysteine and aminoacylase-1

Michael addition–elimination–cyclization based turn-on fluorescence (MADELCY TOF) probes for the highly sensitive estimation of Cys and aminoacylase-1 (ACY-1).

Effect of the ACY-1 gene on HER2 and TRAIL expression in rectal carcinoma

The incidence of rectal carcinoma (RC) is increasing and the age at onset of the disease is reducing. Therefore, elucidating the pathogenesis of RC is beneficial for early diagnosis and improving the prognosis. Aminoacylase-1 (ACY-1) is abnormally expressed in various malignant tumor tissues. Furthermore, the human epidermal growth factor receptor-2 (HER2) gene is involved in tumor metastasis and invasion, while tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces tumor cell apoptosis. The aim of the present study was to investigate the effect of the ACY-1 gene on the expression of HER2 and TRAIL in RC. Cancerous and adjacent tissues from RC patients were collected. ACY-1 expression was analyzed by immunohistochemistry. The rectal cancer cell lines HT29 and SW620, and normal colorectal mucosal epithelial fetal human cells were cultured in vitro. ACY-1 gene and protein expression levels were tested by reverse transcription-quantitative PCR and western blotting. ACY-1 small interfering RNA (siRNA) was transfected into HT29 and SW620 cells. Cell proliferation was detected by thiazolyl blue MTT assay. Caspase-3 activity was assessed using a commercial kit. HER2 and TRAIL expression levels were determined by western blotting. ACY-1 expression was significantly increased in cancer tissue compared with adjacent tissue (P<0.05). ACY-1 expression was elevated in HT29 and SW620 cells compared with normal colorectal mucosal epithelial cells (P<0.05). ACY-1 siRNA transfected into HT29 cells downregulated its expression, inhibited cell proliferation, enhanced caspase-3 activity, reduced HER2 expression and upregulated TRAIL expression (P<0.05). ACY-1 expression was found to be increased in rectal cancer tissue. Therefore, targeting the ACY-1 gene may regulate HER2 and TRAIL expression levels, and may reduce the occurrence and inhibit the development of rectal cancer.

A near-infrared fluorescent probe with large Stokes shift for imaging Cys in tumor mice

Cysteine (Cys), a kind of small molecule biological thiol, not only involves in the regulation of physiological processes, but also is considered a marker of tumor. However, it is challenging to develop suitable probe for detecting Cys in tumors. In this paper, a near-infrared (NIR) fluorescent probe named IX for Cys has been designed and synthesized. The probe shows a NIR emission peak at 770 nm with large Stokes shift (180 nm) upon adding Cys. It displays high sensitivity to Cys with 6-fold increase of fluorescence intensity. Meanwhile, IX has the high selectivity to Cys over other potential interference such as Hcy and GSH, which have similar structure with Cys. In addition, a possible mechanism of fluorescence enhancement is the reaction of IX with Cys to release IX-OH, which is verified by fluorescence spectra, MS and HPLC. Next, IX can selectively image Cys in HCT-116 cells thanks to the low cytotoxicity. Most important of all, the fluorescent probe IX has visualized Cys in HCT116-xenograft tumor mice due to the near-infrared properties with large Stokes shift.

Pathogen detection with electrochemical biosensors: Advantages, challenges and future perspectives

Detection of pathogens, e.g., bacteria and viruses, is still a big challenge in analytical medicine due to their vast number and variety. Developing strategies for rapid, inexpensive, specific, and sensitive detection of the pathogens using nanomaterials, integrating with microfluidics devices, amplification methods, or even combining these strategies have received significant attention. Especially, after the health-threatening COVID-19 outbreak, rapid and sensitive detection of pathogens became very critical. Detection of pathogens could be realized with electrochemical, optical, mass sensitive, or thermal methods. Among them, electrochemical methods are very promising by bringing different advantages, i.e., they exhibit more versatile detection schemes and real-time quantification as well as label-free measurements, which provides a broader application perspective. In this review, we discuss the recent advances for the detection of bacteria and viruses using electrochemical biosensors. Moreover, electrochemical biosensors for pathogen detection were broadly reviewed in terms of analyte, bio-recognition and transduction elements. Different fabrication techniques, detection principles, and applications of various pathogens with the electrochemical biosensors were also discussed.

Iron and nitrogen co-doped graphene quantum dots as highly active peroxidases for the sensitive detection of l-cysteine

New Fe,N co-doped GQDs are easily synthesized and have high peroxidase-mimicking activity for the selective and sensitive colorimetric detection of l-cysteine.

Formation of di-cysteine acrolein adduct decreases cytotoxicity of acrolein by ROS alleviation and apoptosis intervention

Acrolein (ACR) is a toxic contaminant for humans. Our previous research indicated that l-cysteine (Cys) decreased the cytotoxicity of acrolein possibly via adduct formation, but which adduct contributed to the toxicity-lowering effect remains unknown. In this work, we identified a di-cysteine acrolein adduct (ACR-di-Cys) and investigated its toxicity against human bronchial epithelial cell line HBE and colon cancer cell line Caco-2. ACR-di-Cys tremendously decreased acrolein-induced cytotoxicity via alleviating ROS and apoptosis intervention. In the condition of no presence of free cysteine, however, this adduct can convert to mono-ACR-Cys in PBS solution by losing a molecule of cysteine conjugated at CC bond. ACR-mono-Cys showed much higher toxicity than ACR-di-Cys, and even higher than acrolein after 48 h exposure. This study indicated that cysteine can react with acrolein to form adducts with different acrolein-detoxifying capacity, and a sufficient intake of cysteine or cysteine-containing proteins can maximize the detoxifying effect for acrolein via the formation of a highly detoxifying agent, ACR-di-Cys.

Electrochemical substrate for active profiling of cellular surface leucine aminopeptidase activity and drug resistance in cancer cells

Leucine aminopeptidase (LAP) is an essential proteolytic enzyme and potential biomarker for liver malignancy. Overexpression of LAP is directly linked with some fatal physiological and pathological disorders. In this regard, we have designed an activity based electrochemical substrate leucine-benzyl ferrocene carbamate (Leu-FC) for selective profiling of LAP activity in live cells. In practice, LAP instantaneously hydrolyze the Leu residue of the substrate Leu-FC to eliminate the unmasked electrochemical reporter amino ferrocene via predefined self-immolative cascade. The electrochemical signal is distinctly specific for LAP and free of other electroactive biological interference. The substrate Leu-FC empowered sensor displayed broad dynamic range with admirable detection limits. On top of this, the probe Leu-FC was employed in real-time active profiling of cellular LAP activity in HepG2 cells and effect of LAP inhibitor. In extent, the substrate Leu-FC can effectively monitor cisplatin induced overexpression of LAP activity in HepG2 cells in presence and absence of bestatin. The sensor showcased an excellent reliability towards monitoring cellular LAP activity in HepG2 cells. Unlike the traditional antibody-based immunoassays, our approach is capable of monitoring in-situ activity of LAP in live cells.

Smart phone assisted, rapid, simplistic, straightforward and sensitive biosensing of cysteine over other essential amino acids by β-cyclodextrin functionalized gold nanoparticles as a colorimetric probe

Herein, we have attempted the synthesis of β-CD functionalized AuNPs and then applied them as a colorimetric assay for the quantification of Cys over other different essential amino acids.