Protein-Protected Gold Nanocluster-Based Biosensor for Determining the Prooxidant Activity of Natural Antioxidant Compounds

Recent advances in the biomolecules mediated synthesis of nanoclusters for food safety analysis

The development of nanoclusters based on incorporating biomolecules like proteins, lipids, enzymes, DNA, surfactants, and chemical stabilizers creates a stable and high fluorescence bio-sensors promising future due to their high sensitivity, high level of detection and better selectivity. This review addresses a comprehensive and systematic overview of the recent development in synthesizing metal nanocluster by various strategized synthesis techniques. Significantly, the application of nanometal clusters for the detection of various food contaminants such as microorganisms, antibodies, drugs, pesticides, metal contaminants, amino acids, and other food flavors have been discussed briefly concerning the detection techniques, sensitivity, selectivity, and lower limit of detection. The review further gives a brief account on the future prospects in the synthesis of novel metal nanocluster-based biosensors, and their advantages, shortcomings, and potential perspectives toward their application in the field of food safety analysis.

Protamine gold nanoclusters - based fluorescence turn-on sensor for rapid determination of Trinitrotoluene (TNT)

Determination of trace residues of 2,4,6-trinitrotoluene (TNT) is an analytical challenge as it is widely used in military, mining industry, civilian and counter-terrorism purposes. In this study, a gold nanocluster - based turn-on fluorescence sensor was developed for TNT determination. A one-pot approach was used to synthesize the fluorescent protamine - stabilized gold nanoclusters (PRT-AuNC). The proposed turn-on fluorometric sensor relies on the aggregation-induced emission enhancement mechanism. As a result of the donor-acceptor interaction between the non-fluorescent Meisenheimer anion formed from TNT and the amino groups of weakly fluorescent protamine, the PRT-AuNCs aggregate and an accompanying enhancement in fluorescence intensity is observed with a large Stokes shift (λ_ex = 300 nm, λ_em = 600 nm). The fluorescence enhancement increased linearly with TNT with an LOD of 12.44 µg/L. Similar energetic materials, common soil ions and explosive camouflage materials did not affect the proposed fluorometric sensing method. TNT in artificially contaminated soil was determined, and the results were comparable to those obtained by the HPLC-DAD system. The proposed turn-on sensor is an important tool for simple, fast, rapid and sensitive TNT determination, and has a potential to be converted to a kit format.

One‒pot green synthesized protein‒based silver nanocluster as prooxidant biosensor

In this study, silver nanoclusters as prooxidant biosensor were eco‒friendly synthesized using chicken egg white protein without any chemical reducing agents for measuring copper(II)-induced prooxidant activities of catechin, epicatechin, epigallocatechin gallate, resveratrol, gallic acid, chlorogenic acid, and rutin. The prooxidant activities were evaluated via measuring the absorption at 450 nm wavelength of the Cu(I)‒neocuproine chelate formed by extraction of protein-bound Cu(I) with neocuproine reagent. Accuracy was determined by evaluating recovery values of wine, grape and apple samples and the obtained values were between 97.2%‒98.9%. Intra-day precision and inter-day reproducibility experiments were studied with three different experiments in a day and three different days respectively. The obtained relative standard deviation values were 0.96% and 1.91%. The detection limit of the biosensor was found as 0.2 µM. The total prooxidant activities of fresh apple and grape fruits, apple and grape juices, and red wine were determined and the results obtained were compared with the findings of the carbonyl assay. In this study, a cheap, easily applicable, sensitive, and reproducible biosensor was developed. It was seen that it could be used in the measurement of the prooxidant activity of different food samples and give an idea about diet, healthy life, and nutrition.

Exploring the Role of Phytochemicals as Potent Natural Photosensitizers in Photodynamic Therapy

BACKGROUND

Cancer is still considered a deadly disease worldwide due to difficulties in diagnosis, painful treatment procedures, costly therapies, side effects, and cancer relapse. Cancer treatments using conventional methods like chemotherapy and radiotherapy were not convincing due to its post-treatment toxicity in the host. In Photodynamic Therapy (PDT), three individual non-toxic components including a photosensitizer, light source and oxygen cause damage to the cells and tissues when they are combined.

OBJECTIVE

In recent years, phytochemicals are being increasingly recognized as potent complementary drugs for cancer because of its natural availability, less toxicity and therapeutic efficiency in par with commercial drugs. Hence, the idea of using phytochemicals as natural photosensitizers in PDT resulted in a multiple pool of research studies with promising results in preclinical and clinical investigations.

METHODS

In this review, the potential of phytochemicals to act as natural photosensitizers for PDT, their mode of action, drawbacks, challenges and possible solutions are discussed in detail.

RESULTS

In PDT, natural photosensitizers, when used alone or in combination with other photosensitizers, induced cell death by apoptosis and necrosis, increased oxidative stress, altered cancer cell death signaling pathways, increased cytotoxicity and DNA damage in cancer cells. The pro-oxidant nature of certain antioxidant polyphenols, hormesis phenomenon, Warburg effect and DNA damaging potential plays a significant role in the photosensitizing mechanism of phytochemicals in PDT.

CONCLUSION

This review explores the role of phytochemicals that can act as photosensitizers alone or in combination with PDT and its mechanism of action on different cancers.

Diagnosis of cancer at early stages based on the multiplex detection of tumor markers using metal nanoclusters

Traditional cancer diagnosis strategies are not considered by most people until the last resort, which delays many cancer treatments leading to advanced stages. Tumor marker sensors show great potential for detecting cancer because of its cost-effective and harmless checking procedures. Normally, one tumor marker is detected each time by using one type of sensor, but the accuracy to declare cancer is not always satisfied. Metal nanoclusters are ultra-small nanomaterials with low toxicity, distinct optical properties, catalytic activities, and cost-effective performance. Some metal nanoclusters have been designed to detect more than one tumor marker in a single step. The consideration of combined parameters using such facile sensing strategies has the potential to simplify the test procedure, and increase the diagnostic accuracy of early cancer. Therefore, various sensing strategies for the multiplex detection of tumor markers using metal nanoclusters are summarized.

Ultrasmall Au and Ag Nanoclusters for Biomedical Applications: A Review

Noble metal (e.g., Au, Ag, Pt, Pd, and their alloys) nanoclusters (NCs) have emerged as a new type of functional nanomaterial in nanoscience and nanotechnology. Owing to their unique properties, such as their ultrasmall dimension, enhanced photoluminescence, low toxicity, and excellent biocompatibility, noble metal NCs-especially Au and Ag NCs-have found various applications in biomedical regimes. This review summarizes the recent advances made in employing ultrasmall Au and Ag NCs for biomedical applications, with particular emphasis on bioimaging and biosensing, anti-microbial applications, and tumor targeting and cancer treatment. Challenges, including the shared and specific challenges for Au and Ag NC toward biomedical applications, and future directions are briefly discussed at the end.

Natural protein-templated fluorescent gold nanoclusters: Syntheses and applications

For the past decades, the synthesis of metal nanoclusters has been a great interest for research, for their unique physicochemical properties and great contributions to the catalytic, electrical and biomedical applications. Protein-templated gold nanoclusters (AuNCs) is a kind of fluorescent nanomaterials with good solubility, excellent stability, biocompatibility, decent quantum yields and active groups (-COOH, -NH₂) for facilitating modifications. Natural proteins are easily available, commercially affordable, diverse and multitudinous in animals, plants and foods, which provide a template pool for the exploration of AuNCs. This is one of the few reviews of specifically focusing on the natural protein-templated fluorescent AuNCs. The syntheses, properties and applications of different AuNCs were enumerated. Prospects were given on utilizing structure-modified proteins, bioactive enzymes, antibodies which should endow the AuNCs more favourable fluorescence performances and functional characteristics. The applications of AuNCs in analytical, biomedical and food sciences would be further heightened.

A novel gold nanocluster-based fluorometric biosensor for measuring prooxidant activity with a large Stokes shift

A chicken egg white protein-protected gold nanocluster (CEW-AuNC) based fluorogenic biosensor, where protein was used as both reducing and protecting agent, was developed to determine the Cu(II)-induced prooxidant activity of natural antioxidants abundant in food and biological samples. Gold nanoclusters, prepared using egg white proteins, exhibited strong fluorescence. The prooxidant activity of the tested antioxidants was indirectly measured by their reducing action on Cu(II) to Cu(I), and the reduced cuprous ion was bound to the thiol groups in the CEW-AuNC structure, causing a decrease in fluorescence intensity. Epicatechin, catechin, epigallocatechin gallate, morin, rutin, quercetin, gallic, chlorogenic, and rosmarinic acids, glutathione, cysteine, N-acetyl cysteine, bilirubin, resveratrol, and α-tocopherol were studied as natural antioxidants. A fluorometric method showing a large Stokes shift with excitation/emission maxima at 360∕640 nm was developed to sensitively measure the decrease in the fluorescence of CEW-AuNC associated with the binding of copper(I) to the protein structure. Total prooxidant activities of the binary, ternary, and quaternary synthetic mixtures and of some food and synthetic serum samples were determined. The biosensor response was statistically compared to that of its spectrophotometric counterpart. This method can be used for the control of the oxidative stability of foods with a prolonged shelf life.

Current Issues in Antioxidant Measurement

The rationale and scope of the main issues of antioxidant measurement are presented, with basic definitions and terms in antioxidant research (such as reactive species and related antioxidative defenses, oxidative stress, and antioxidant activity and capacity) in a historical background. An overview of technical problems and expectations is given in terms of interpretation of results, precision and comparability of methods, capability of simulating physical reality, and analytical performance (sensitivity, selectivity, etc.). Current analytical methods for measuring antioxidant and antiradical activity are classified from various viewpoints. Reaction kinetics and thermodynamics of current analytical methods are discussed, describing physicochemical aspects of antioxidant action and measurement. Controversies and limitations of the widely used antioxidant assays are elaborated in detail. Emerging techniques in antioxidant testing (e.g., nanotechnology, sensors, electrochemistry, chemometry, and hyphenated methods) are broadly introduced. Finally, hints for the selection of suitable assays (i.e., preferable for a specific purpose) and future prospects are given.