Label-free fluorometric detection of chymotrypsin activity using graphene oxide/nucleic-acid-stabilized silver nanoclusters hybrid materials

Fluorescent DNA-Silver nanoclusters in food safety detection: From synthesis to application

In recent years, the conventional preparation of silver nanoclusters (AgNCs) has attracted much attention due to their ultra-small size, tunable fluorescence, easy-to-engineer, as well as biocompatible material. Moreover, its great affinity towards cytosine bases on single-stranded DNA has led to the construction of biosensors, especially aptamers, for a broad variety of applications in food safety and environmental protection. In past years, numerous researchers paid attention to the construction of AgNCs aptasensor. Therefore, this review will be an effort to summarize the synthetic strategy along with the influences of factors on synthesis, categorize the sensing mechanism of aptamer-functionalized AgNCs biosensors, as well as their specific applications in food safety detection including heavy metal, toxin, and foodborne pathogenic bacteria. Furthermore, a brief conclusion and outlook regarding the prospects and challenges of their applications in food safety were drawn in line with the developments in DNA-AgNCs.

Highly Sensitive Detection of Chymotrypsin Based on Metal Organic Frameworks with Peptides Sensors

In this study, peptides and composite nanomaterials based on copper nanoclusters (CuNCs) were used to detect chymotrypsin. The peptide was a chymotrypsin-specific cleavage peptide. The amino end of the peptide was covalently bound to CuNCs. The sulfhydryl group at the other end of the peptide can covalently combine with the composite nanomaterials. The fluorescence was quenched by fluorescence resonance energy transfer. The specific site of the peptide was cleaved by chymotrypsin. Therefore, the CuNCs were far away from the surface of the composite nanomaterials, and the intensity of fluorescence was restored. The limit of detection (LOD) using Porous Coordination Network (PCN)@graphene oxide (GO) @ gold nanoparticle (AuNP) sensor was lower than that of using PCN@AuNPs. The LOD based on PCN@GO@AuNPs was reduced from 9.57 pg mL^-1 to 3.91 pg mL^-1. This method was also used in a real sample. Therefore, it is a promising method in the biomedical field.

A Novel Fluorescence Aptasensor Based on Magnetic Beads/Gold Nanoparticles/DNA-Stabilized Silver Nanoclusters for Detection of Salmonella Typhimurium

Salmonella Typhimurium (S. Typhimurium) is a globally distributed foodborne pathogen, which can lead to outbreaks of foodborne infectious diseases. It is essential to guarantee food safety by timely and correct detection of S. Typhimurium. In this investigation, an original fluorescence aptasensor was constructed to detect S. Typhimurium rapidly and sensitively. Through the coupling of magnetic beads, aptamer, and gold nanoparticles (AuNPs), a fluorescence quenching system with a "sandwich structure" was established. The aptamer acted as a link, and its specific binding to S. Typhimurium could release AuNPs from the system. Meanwhile, fluorescent DNA-stabilized silver nanoclusters (DNA-AgNCs) were synthesized. The fluorescence intensity changes caused by the fluorescence resonance energy transfer between DNA-AgNCs and AuNPs were utilized to detect S. Typhimurium. The purposed aptasensor exhibited high selectivity and sensitivity with a linear response to S. Typhimurium, ranging from 3.7 × 10² to 3.7 × 10⁵ cfu/mL. The limit of detection (LOD) was estimated to be 98 cfu/mL within 2 h 10 min. In addition, this method showed excellent application for detection of S. Typhimurium in artificially contaminated milk, with LOD reaching 3.4 × 10² cfu/mL. Therefore, the developed fluorescence aptasensor has great potential to identify S. Typhimurium in foodstuffs.

Activatable endoplasmic reticulum-targeted NIR fluorescent probe with a large Stokes shift for detecting and imaging chymotrypsin

In this work, the first endoplasmic reticulum-targeted near-infrared fluorescent probe, ISO-Chy, with a large Stokes shift is reported by introducing a recognition group of 4-bromobutyl for chymotrypsin detection.

Graphene oxide-based fluorescent biosensors and their biomedical applications in diagnosis and drug discovery

Graphene oxide (GO), an oxidized derivative of graphene, has received much attention for developing novel fluorescent bioanalytic platforms due to its remarkable optical properties and biocompatibility. The reliable performance and robustness of GO-based biosensors have enabled various applications in the biomedical field including diagnosis and drug discovery. Here, recent advances in the development of GO-based fluorescent biosensors are overviewed, particularly nucleic acid detection and enzyme activity assay. In addition, practical applications in biomarker detection and high-throughput screening are also examined. Lastly, basic design principles and remaining challenges of these types of biosensors are discussed for further progress.

A structurally precise AgxAu25-x nanocluster based cancer theranostic platform with tri-targeting/in situ O2-generation/aggregation enhanced fluorescence imaging/photothermal-photodynamic therapies

The photothermal and photodynamic performances of structurally precise oil-soluble AgxAu25-x (x ≤ 13) nanoclusters were first explored and they were solubilized into new assemblies to form a versatile cancer theranostic platform with tri-targeting/in situ O2-generation/aggregation enhanced fluorescence imaging/photothermal-photodynamic therapy effects, which will provide an important reference for precision theranostics at the atomic level in future.

The detection of chymotrypsin using peptides covalent bound to the surface of graphene oxide and gold nanoparticles

In this study, pyrene was used as a fluorescent dye for peptides.

Perspective on chymotrypsin detection

Chymotrypsin is one of the most extensively known proteases participating in the pathogenesis of various diseases, which can be used in drug discovery and clinical diagnosis.

Endogenous Cys-Assisted GSH@AgNCs-rGO Nanoprobe for Real-Time Monitoring of Dynamic Change in GSH Levels Regulated by Natural Drug

Glutathione (GSH) levels are closely related to the homeostasis of redox state which directly affects human disease occurrence by regulating cell apoptosis. Hence, real-time monitoring of dynamic changes in intracellular GSH levels is urgently needed for disease early diagnosis and evaluation of therapy efficiency. In this study, an endogenous cysteine (Cys)-assisted detection system based on GSH@AgNCs and reduced graphene oxide (rGO) with high sensitivity and specificity was developed for GSH detection. Compared with GSH, GSH@AgNCs with weaker affinity and bonding force was quite easier to extrude from the rGO surface when competing against GSH, leading to the obvious change in fluorescence signal. This phenomenon was termed as "a crowding out effect". Furthermore, the presence of Cys can improve GSH assay sensitivity by enhancing the quenching efficiency of rGO on the GSH@AgNCs. In vitro assay indicated that the efficiency of fluorescence recovery was positively related with GSH concentration in the range from 0 to 10 mM. In addition, the method was employed for real-time monitoring of the dynamic changes in GSH levels regulated by natural drugs. The imaging results showed that the natural compound 3 (C3) can downregulate GSH levels in HepG2 cells, which was accompanied by reactive oxygen species (ROS) release and apoptosis induction. Finally, the method was used to monitor the change of GSH levels in serum samples with chronic hepatitis B (CHB) infection. The results demonstrated that the occurrence and development of CHB may be positively correlated with GSH levels to some extent. Overall, the above results demonstrate the potential application of this new nanosystem in anticancer natural drug screening and clinical assay regarding GSH levels.

A glassy carbon electrode modified with graphene oxide, poly(3,4-ethylenedioxythiophene), an antifouling peptide and an aptamer for ultrasensitive detection of adenosine triphosphate

An antifouling aptasensor is described for voltammetric determination of adenosine triphosphate (ATP). A glassy carbon electrode (GCE) was modified with a graphene oxide and poly(3,4-ethylenedioxythiophene) (GO-PEDOT) composite film by electrodeposition. Next, the zwitterionic peptide (EKEKEKE) was attached. It forms an antifouling layer on the modified GCE and serves as the support for subsequent aptamer immobilization. The resulting aptasensor typically is operated at a potential of 0.18 V (vs. SCE) using hexacyanoferrate as the electrochemical probe. It has a linear response in the 0.1 pM to 1.0 μM ATP concentration range, a 0.03 pM detection limit and a sensitivity of 2674.7 μA·μM^-1·cm^-2. It has outstanding selectivity, satisfactory reproducibility and desired stability. It was used to quantify ATP in ATP-spiked 10% serum solutions. Graphical abstract Schematic presentation of the construction of the aptamer based electrode for voltammetric determination of ATP.

A non-peptide NIR fluorescent probe for detection of chymotrypsin and its imaging application

A novel non-peptide NIR fluorescent probe for the detection of chymotrypsin and its imaging application.

Identifying three routes of the sensing mechanism for casein-directed gold nanoclusters

Although there have existed kinds of gold nanoclusters (AuNCs) employed for various sensing purposes, scarce studies were proposed for systematically exploring their multiple routes of the sensing mechanism since that plays the critical role for broadening their analysis applications. Herein, casein-directed gold nanoclusters (AuNCs@casein) have been successfully raised for identifying their multiple routes towards the sensing mechanism. Initially, the current nanoclusters were synthesized in aqueous solution with a quantum yield of nearly 2.1%, which obviously showed the red fluorescence at 600 nm. Subsequently, we have explored three routes of quenching the fluorescence of AuNCs@casein by introducing thiourea, bromelain, and graphene oxide with amino groups (GO-NH₂) as the representatives. To be specific, the formed bonds of Au-S between thiourea and AuNCs@casein achieved to quench their fluorescence, and the templates of AuNCs@casein destroyed by bromelain also showed the dramatically decreased fluorescence, and the energy transferring from the current AuNCs to GO-NH₂ indeed lead to the fluorescent variations of AuNCs@casein. On the basis of these phenomena, AuNCs@casein was further applied for simply sensing thiourea, bromelain and GO-NH₂ through the standard formats. Significantly, this study elaborated three quenching routes of AuNCs@casein and may provide more sensing strategies for other types of nanoclusters.

Detection of chymase activity using a specific peptide probe conjugated onto gold nanoparticles

The gold nanoparticles (AuNPs) peptide probe functionalized with specific peptide sequences was developed for the sensitive and efficient detection of chymase activity.

Thiolated DNA-templated silver nanoclusters with strong fluorescence emission and a long shelf-life

Thiolated DNA (DNA-SH) was employed as a template in the synthesis and stabilization of AgNCs (DNA-SH-AgNCs). Resulting from the synergistic protective effect of specific Ag⁺-DNA interactions and Ag-S bonding, DNA-SH-AgNCs exhibited high quantum yields and resistance to oxidation.