Fluorescence turn-off detection of spermine in biofluids using pepsin mediated synthesis of gold nanoclusters as a probe

"Turn-on" and pinhole-free ultrathin core-shell Au@SiO2 nanoparticle-based metal-enhanced fluorescent (MEF) chemodosimeter for Hg2

This study reports a metal-enhanced fluorescence chemodosimeter for highly sensitive detection of Hg2+ ions. Silica-coated Au nanoparticles (Au@SiO2 NPs) with a pinhole-free 4-5 nm shell were synthesized and functionalized with a monolayer of turn-on fluorescent probes. Compared to other organic fluorescent probes suffering from poor biocompatibility and detection limits, this design of a monolayer of turn-on fluorescent probes immobilized on the Au@SiO2 NPs with a pinhole-free 4-5 nm shell avoids fluorescence quenching and allows the fluorescent probe within the field of the inner Au NPs to experience metal-enhanced fluorescence. With this design, the chemodosimeter permits fluorescence emission in the presence of Hg2+ ions, because they trigger the ring-opening reaction of the fluorescent probe immobilized on the Au@SiO2 NPs. Additionally, the fluorescent probe is distanced by the thin SiO2 shell from directly attaching to the metallic Au NPs, which not only avoids fluorescence quenching but allows the fluorescent probe within the long-ranged field of the inner Au NPs to experience metal-enhanced fluorescence. As a result, the detection limit for the chemodosimeter can reach up to 5.0 × 10-11 M, nearly two orders of magnitude higher than that achieved for the free fluorescent probe. We also demonstrate the acquisition of images of Hg2+ in HTC116 cells and zebrafish using a simple fluorescence confocal imaging technique. The fluorescence response results for HTC116 cells and zebrafish show that the probes can permeate into cells and organisms. Considering the availability of the many organic fluorescent probes that have been designed, the current designed metal-enhanced fluorescence chemodosimeter holds great potential for fluorescence detection of diverse species and fluorescence imaging.

Machine Learning-Assisted High-Throughput Strategy for Real-Time Detection of Spermine Using a Triple-Emission Ratiometric Probe

In this study, we designed and fabricated a spermine-responsive triple-emission ratiometric fluorescent probe using dual-emissive carbon nanoparticles and quantum dots, which improve the sensor's accuracy and reduce interfering environmental effects. The probe is advantageous for the proportionate detection of spermine because it has good emission resolution, and the maximum points of the two emission peaks differ by 95 nm. As a proof of concept, cuvettes and a 96-well plate were combined with a smartphone and YOLO series algorithms to accomplish real-time, visual, and high-throughput detection of seafood and meat freshness. In addition, the reaction mechanism was verified by density functional theory and fundamental characterizations. Upon exposure to different amounts of spermine, the intensity of the fluorescent probe changed linearly, and the fluorescent color shifted from yellow-green to red, with a limit of detection of 0.33 μM. To enable visual identification of food-originated spermine, a hydrogel-based visual sensing platform was successfully developed utilizing the triple-emission fluorescent probe. Consequently, spermine could be identified and quantified without complicated equipment.

Protein-Templated Metal Nanoclusters: Molecular-like Hybrids for Biosensing, Diagnostics and Pharmaceutics

The use of proteins as biomolecular templates to synthesize atomically precise metal nanoclusters has been gaining traction due to their appealing properties such as photoluminescence, good colloidal- and photostability and biocompatibility. The synergistic effect of using a protein scaffold and metal nanoclusters makes it especially attractive for biomedical applications. Unlike other reviews, we focus on proteins in general as the protective ligand for various metal nanoclusters and highlight their applications in the biomedical field. We first introduce the approaches and underlined principles in synthesizing protein-templated metal nanoclusters and summarize some of the typical proteins that have been used thus far. Afterwards, we highlight the key physicochemical properties and the characterization techniques commonly used for the size, structure and optical properties of protein-templated metal nanoclusters. We feature two case studies to illustrate the importance of combining these characterization techniques to elucidate the formation process of protein-templated metal nanoclusters. Lastly, we highlight the promising applications of protein-templated metal nanoclusters in three areas-biosensing, diagnostics and therapeutics.

Selective determination of ellagic acid in aqueous solution using blue-green emissive copper nanoclusters

Development of beneficial sensors to analyze ellagic acid concentrations is of great importance for food safety and human health. Herein, a facile and fast fluorescent probe was carried out for the excellently selective and sensitive measurement of ellagic acid in real samples through histidine protected copper nanoclusters (histidine@Cu NCs) as a nanosensor. This as-developed histidine@Cu NCs were performed through UV-vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and fluorescence lifetime analysis. The TEM image revealed that this nanomaterial had spherical features with the average diameter of 2.5 ± 0.05 nm. The blue-green fluorescence of this Cu NCs was found under the UV light. Meanwhile, the maximum excitation and emission wavelength were located at 387 nm and 488 nm. After addition of ellagic acid, the fluorescence of histidine@Cu NCs was slowly weakened with excellent linear range of 0.5-300 μM and detection limit of 0.077 μM. The fluorescence weakening mechanism of this nanosensor were attributed to the inner filter effect (IFE) and static quenching. Finally, this as-established analysis platform was successfully employed to measure ellagic acid in real samples.

Perspectives of different colour-emissive nanomaterials in fluorescent ink, LEDs, cell imaging, and sensing of various analytes

In the past 2 decades, multicolour light-emissive nanomaterials have gained significant interest in chemical and biological sciences because of their unique optical properties. These materials have drawn much attention due to their unique characteristics towards various application fields. The development of novel nanomaterials has become the pinpoint for different application areas. In this review, the recent progress in the area of multicolour-emissive nanomaterials is summarized. The different emissions (white, orange, green, red, blue, and multicolour) of nanostructure materials (metal nanoclusters, quantum dots, carbon dots, and rare earth-based nanomaterials) are briefly discussed. The potential applications of different colour-emissive nanomaterials in the development of fluorescent inks, light-emitting diodes, cell imaging, and sensing devices are briefly summarized. Finally, the future perspectives of multicolour-emissive nanomaterials are discussed.

Fluorescent folic acid-capped copper nanoclusters for the determination of rifampicin based on inner filter effect

Development of excellent sensors to determine trace concentrations of rifampicin is of intense importance for medicine analysis and human health. Herein, a facile and green fluorescent probe was established for the determination of rifampicin by using folic acid protected copper nanoclusters (FA-Cu NCs). Many characterization methods were applied for the analysis of the as-prepared FA-Cu NCs including UV-visible absorption spectra, fluorescence spectra, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), fluorescence lifetime and X-ray photoelectron spectroscopy (XPS). The TEM image suggested that the as-prepared FA-Cu NCs were highly dispersed. The as-synthesized FA-Cu NCs emerged blue fluorescence under UV light and demonstrated maximum emission wavelength at 446 nm under the maximum excitation wavelength of 358 nm. After the addition of rifampicin, the FL intensities of FA-Cu NCs were uncommonly quenched. The related experimental data intimated that the quenching mechanisms were assumed to the inner filter effect (IFE) and static quenching. The as-proposed probe platform displayed an obvious linear relationship with rifampicin concentrations varying from 0.5 to 100 µM, and the corresponding detection limit (LOD) was 0.073 µM (S/N = 3). Finally, the as-established detection platform was successfully employed to analyze trace concentrations of rifampicin in real samples.

Fabrication of a ratiometric electrochemiluminescence biosensor using single self-enhanced nanoluminophores for the detection of spermine

A ratiometric electrochemiluminescence strategy using a single luminophore for accurate and sensitive biomolecule detection could be immensely valuable in bioanalysis. Herein, an ultrasensitive ratiometric electrochemiluminescence sensing system was fabricated using a self-enhanced luminophore with dual-signal emission for the detection of spermine. A nanocomposite was synthesized by the covalent attachment of N, N-diisopropylethylenediamine onto glutathione-protected Au-Ag bimetallic nanoclusters (DPEA-GSH@Au/Ag BNCs). The nanocomposite exhibited efficient intra-cluster charge transfer to produce strong anodic self-enhanced electrochemiluminescence emission at 0.8 V without external co-reactants. Interestingly, the DPEA@GSH@Au-Ag BNCs exhibited cathodic electrochemiluminescence emission upon the addition of the co-reactant potassium persulfate at -1.6 V, exhibiting stable and efficient dual-signal electrochemiluminescence emission features at a continuous potential window of -1.75 to 1.2 V. Thus, they were used to fabricate a single-luminophore electrochemiluminescence sensor with dual emission. The cathodic emission of the biosensor gradually increased with increasing concentrations of spermine, whereas the anodic electrochemiluminescence intensity remained almost constant, enabling the ratiometric detection of spermine. The fabricated biosensor, with an internal standard, significantly improved the accuracy and reliability of spermine detection in a wide concentration range of 0.85 pM-100 μM, with a low limit of detection of 0.12 pM (S/N = 3) under optimum conditions. This single-luminophore electrochemiluminescence sensing system could be used for the detection of spermine and could guide the construction of ratiometric electrochemiluminescence sensors in the future.

Synthesis of blue fluorescent molybdenum nanoclusters with novel terephthaldehyde-cysteine Schiff base for detection of pyrophosphate

In this work, terephthaldehyde-cysteine-molybdenum nanoclusters (TPA-Cys-MoNCs) were synthesized by using terephthaldehyde-cysteine (TPA-Cys) Schiff base as a novel ligand. The as-synthesized TPA-Cys-MoNCs showed blue fluorescence under UV lamp at 365 nm, displaying emission peak at 455 nm when excited at 340 nm. The fluorescent TPA-Cys-MoNCs are used as a probe for sensitive assay of pyrophosphate (PPi) via fluorescence quenching mechanism. The emission peak intensity of TPA-Cys-MoNCs at 455 nm exhibited a linear quenching with increasing amount of PPi. As a result, quantitative assay was developed for the detection of PPi (0.01-200 µM) with the detection limit of 0.9 nM. The developed probe was successfully demonstrated for the detection of PPi in biofluids (urine and plasma).

Recent Advances in Fluorescent Methods for Polyamine Detection and the Polyamine Suppressing Strategy in Tumor Treatment

The biogenic aliphatic polyamines (spermine, spermidine, and putrescine) are responsible for numerous cell functions, including cell proliferation, the stabilization of nucleic acid conformations, cell division, homeostasis, gene expression, and protein synthesis in living organisms. The change of polyamine concentrations in the urine or blood is usually related to the presence of malignant tumors and is regarded as a biomarker for the early diagnosis of cancer. Therefore, the detection of polyamine levels in physiological fluids can provide valuable information in terms of cancer diagnosis and in monitoring therapeutic effects. In this review, we summarize the recent advances in fluorescent methods for polyamine detection (supramolecular fluorescent sensing systems, fluorescent probes based on the chromophore reaction, fluorescent small molecules, and fluorescent nanoparticles). In addition, tumor polyamine-suppressing strategies (such as polyamine conjugate, polyamine analogs, combinations that target multiple components, spermine-responsive supramolecular chemotherapy, a combination of polyamine consumption and photodynamic therapy, etc.) are highlighted. We hope that this review promotes the development of more efficient polyamine detection methods and provides a comprehensive understanding of polyamine-based tumor suppressor strategies.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

Polymer-capped gold nanoparticles as nanozymes with improved catalytic activity for the monitoring of serum ciprofloxacin

More recently, gold nanoparticle (AuNP)-based nanozymes have become one of the burgeoning research hot topics. However, few studies have focused on these AuNP-nanozymes with polymers as ligands. A significant challenge is to reveal their catalytic mechanism and to improve their catalytic activity by changing the structures of the polymers. In this study, polyacrylamide (PAM) with different chain lengths was synthesized and used as the ligand to prepare PAM@AuNPs. The resultant nanozymes exhibited good peroxidase-like activity for catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂). In particular, due to the electrostatic interaction between the negatively charged PAM@AuNPs and the positively charged drug, the addition of ciprofloxacin in the oxidation system induced the aggregation of PAM@AuNPs and produced more amount of reactive oxygen species, which greatly promoted the catalytic activity of PAM@AuNPs. Inspired by the attractive property, a highly selective and sensitive colorimetric assay for the monitoring of ciprofloxacin was created. A good linear relationship between the UV-Vis absorption intensity of PAM@AuNPs-TMB-H₂O₂ at 650 nm wavelength and the ciprofloxacin concentration was observed ranging from 1.0 μM to 12.0 μM (R² = 0.998), providing the detection limit of 0.5 μM. The ciprofloxacin metabolism was further studied in rats. It reveals great potential of polymer protected AuNP-nanozymes in practical drug analysis.

Sustainable chemistry approach for the preparation of bluish green emissive copper nanoclusters from Justicia adhatoda leaves extract: a facile analytical approach for the sensing of myoglobin and l-thyroxine

Sustainable chemistry approach for synthesis of fluorescent copper nanoclusters for sensing of myoglobin and l-thyroxine.

Facile and Sensitive Detection of Nitrogen-Containing Organic Bases with Near Infrared C-Dots Derived Assays

In this article, we have designed both colorimetric (including solution and test paper type) and spectral sensors (including UV-vis and PL type) for the quick and sensitive detection of general nitrogen-containing organic bases (NCOBs); the limit of detection could reach as low as 0.50 nM. NCOBs included 11 examples, covering aliphatic and aromatic amines, five- and six-membered heterocyclics, fused-ring heterocyclics, amino acids, and antibiotics. Furthermore, the assays demonstrated high reliability in sensing NCOBs and excellent ability to distinguish NCOBs from oxygen and sulfur containing organics. The assays developed could find important applications for the detection of NCOBs in the fields of biomedicine, chemistry, and agriculture.

Supramolecular imaging of spermine in cancer cells

As an important biomarker, the overexpressed spermine has been widely investigated for cancer diagnosis and treatment. However, bioimaging of spermine in living cells is still a formidable challenge. Herein, we design a supramolecular imaging ensemble for spermine by the host-guest complexation of amphiphilic sulfonatocalix[5]arene (SC5A12C) assembly with lucigenin (LCG). Strong binding ability and complexation-induced fluorescence quenching properties enable SC5A12C to quench the fluorescence of LCG dramatically and to recover it completely due to the competition of overexpressed spermine in cancer cells. SC5A12C also exhibits excellent biocompatibility and promotes cellular uptake due to its ability to form ultra-stable assembly. Co-assembling folate further promotes the cellular uptake of folate receptor overexpressed cancer cells, contributing to enhanced bioimaging.

Gold nanoclusters: An ultrasmall platform for multifaceted applications

Gold nanoclusters (Au NCs) with a core size below 2 nm form an exciting class of functional nano-materials with characteristic physical and chemical properties. The properties of Au NCs are more prominent and extremely different from their bulk counterparts. The synthesis of Au NCs is generally assisted by template or ligand, which impart excellent cluster stability and high quantum yield. The tunable and sensitive physicochemical properties of Au NCs open horizons for their advanced applications in various interdisciplinary fields. In this review, we briefly summarize the solution phase synthesis and origin of the characteristic properties of Au NCs. A vast review of recent research work introducing biosensors based on Au NCs has been presented along with their specifications and detection limits. This review also highlights recent progress in the use of Au NCs as bio-imaging probe, enzyme mimic, temperature sensing probe and catalysts. A speculation on present challenges and certain future prospects have also been provided to enlighten the path for advancement of multifaceted applications of Au NCs.

In-tube solid phase microextraction coupled to miniaturized liquid chromatography for both, noble metal nanoparticle assessment and sensitive plasmonic assay development

Colorimetric localized surface plasmon resonance (LSPR) as analytical response is applied for a wide number of chemical sensors and biosensors. However, the dependence of different factors, such as size distribution of nanoparticles (NPs), shape, dielectric environment, inter-particle distance and matrix, among others, can provide non-reliable results by UV-vis spectrometry in complex matrices if NP assessment is not carried out, particularly at low levels of analyte concentrations. Miniaturized liquid chromatography, capillary (CapLC) and nano (NanoLC), coupled on line with in-tube solid phase microextraction (IT-SPME) is proposed for the first time for both, controlling suitability of used noble metal NP dispersions and developing plasmonic assays. Several capped noble NPs and target analytes were tested from variations in the chromatographic profiles obtained by using diode array detection. The IT-SPME step, which influenced the chromatographic fingerprint provided by noble NP dispersions, was studied by asymmetrical flow field flow fractionation (AF4) too. We monitored NP aggregation induced by interaction with several analytes like acids and spermine (SPN). Assessment of NPs was achieved in less than 10 min and it permitted to develop suitable plasmonic tests. Here, it was also demonstrated that these assays can be followed by IT-SPME-miniaturized LC-DAD and more sensitivity and selectivity than those provided by UV-Vis spectrometry were achieved. Analysing urine samples to determine SPN as a cancer biomarker as a proof of concept is presented.

Silver-enhanced fluorescence of bimetallic Au/Ag nanoclusters as ultrasensitive sensing probe for the detection of folic acid

Folic acid (FA) is the natural form of water-soluble vitamins widely found in most plants and animal products and its deficiency leads to several human body abnormalities. The advancements of metal nanoclusters are highly increasing due to their molecule-like optical properties and attractive applications. Because of increasingly demand of noble metal nanoclusters as sensing templates, different synthesis methods have been developed for facile synthesis of noble metal nanoclusters. Herein, red-emitting fluorescent bovine serum albumin (BSA)-capped Au-Ag bimetallic NCs are facilely synthesized through green one-pot synthetic approach. The effect of silver on the fluorescence properties of Au NCs was investigated and it was found that introduction of silver can enhance the fluorescence intensity. The fluorescence intensity of the as-prepared Au-Ag nanoclusters gets quenched in the presence of folic acid in an aqueous medium and it was used as ultrasensitive sensing probe for FA detection. The developed Au-Ag NCs-based sensing probe shows linear response in the wide range of 0-100 μM and the detection limit is as low as 0.47 nM. Its applicability has also been confirmed successfully in real human serum, urine and FA tablet samples. Due to the high stability, sensitivity and selectivity, the developed bimetallic cluster sensing system is highly promising to be applied in the pharmaceutical and clinical laboratories.

A rapid, simple and ultrasensitive spectrofluorimetric method for the direct detection of metformin in real samples based on a nanoquenching approach

Metformin (MET), as an oral antidiabetic and antihyperglycemic agent, is widely used to treat type II diabetes mellitus. Because of its increasing consumption, developing a fast, simple, and selective method to determine its concentration in biological samples (serum and urine) and pharmaceutical formulations (tablets) is of great interest. In this study, we used a FRET-based fluorescent nanosensor (Tb-phen-AgNPs system) for sensitive detection of MET in tablet and serum samples. This method is based on the enhancing effect of MET on the emission intensity of the Tb-phen complex, which is quenched by AgNPs via energy transfer process (turn off-on mode). A good linear relationship between the MET concentration and enhanced emission intensity of the Tb-phen-AgNPs system was observed in the range of (0.75-3.7) × 10^-6 M under optimum conditions. Limit of detection and limit of quantitation were calculated to be 0.43 × 10^-6 M and 1.31 × 10^-6 M, respectively. This method was successfully used to determine MET concentrations in pharmaceutical dosage form and in spiked serum sample. The obtained recoveries from pharmaceutical formulation and serum sample were in the range 86.75-98.97% and 85.10-100.96%, respectively. Collectively, our results indicated that the method described here is simple, sensitive, cost effective, and free from interference. Therefore, it can be used as an effective and routine method for the direct and rapid determination of MET levels in biological samples such as serum.

A Sensitive, Simple and Direct Determination of Pantoprazole Based on a "Turn off-on" Fluorescence Nanosensor by Using Terbium-1,10-phenanthroline-silver Nanoparticles

A new sensitive, simple, rapid, reliable and selective fluorometric method for the determination of pantoprazole (PAN) in human plasma and a pharmaceutical formulation has been developed. This technique is based on a quenching effect of silver nanoparticles (AgNPs) on the emission intensity of a fluorescent probe, terbium(III)-1,10-phenantroline (Tb(III)-phen) complex (due to a fluorescence resonance energy transfer (FRET) phenomenon between the Tb(III)-phen complex and AgNPs), and then restoring the fluorescence intensity of the Tb(III)-phen-AgNPs system upon the addition of PAN (turn off-on process). The effects of various factors on the proposed method including time, temperature, pH, order of the addition of various reagents and the concentration of AgNPs were investigated. Under the optimal conditions, a good linear relationship between the enhanced emission intensity of the Tb(III)-phen-AgNPs system and the PAN concentration was observed in the range of (10 - 1000) × 10^-8 M. The limit of detection (LOD) and the limit of quantitation (LOQ) were 7.2 × 10^-8 and 24.2 × 10^-8 M, respectively. Also, the interferences of some common interfering species on the fluorescence intensity of the system were investigated. This simple and sensitive method was successfully applied for the determination of PAN in spiked human plasma samples and in its capsule formulation. The analytical recoveries were in the range of 88.54 - 101.33 and 90.07 - 98.85%, respectively.

Advances in biomedical and pharmaceutical applications of protein-stabilized gold nanoclusters

The interest in using gold nanoclusters (AuNCs) as imaging probes is growing, covering wide ranges of applications. The stabilization of AuNCs with protein ligands enhances their biomedical and pharmaceutical applications. This is due to the biocompatibility, water solubility and bioactivity of proteins. Different factors can control the optical properties of AuNCs such as protein size, amino acids content and conformational structure. Controlling the synthesis conditions can result in tuning the AuNCs excitation, emission, fluorescence intensity and physicochemical properties to fulfill different applications. NIR-emitting protein-stabilized AuNCs are promising as imaging agents for targeting and visualization of cancer in vitro and in vivo. They are promising to be included as an important part of multifunctional theranostic nanosystems, due to their potential dual functions as imaging and photosensitizing agent for photodynamic therapy. Additionally, the protein around AuNCs represents a rich environment of active functional groups that are susceptible for conjugation with various biomolecules. Protein-AuNCs can act as fluorescent probes for rapid and selective analysis of different analytes in solution, cells or biological fluids. In conclusion, the variability of protein-AuNC applications can advance research in different biomedical and pharmaceutical fields.

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 review on chemical and electrochemical methodologies for the sensing of biogenic amines

Biogenic amines (BA) are biomolecules of low molecular weight with organic basic functionalities (amine group) that are formed by the microbial decarboxylation of amino acids of fermented food/beverages. Hence BAs are an important indicator in estimating the freshness and quality of meat, seafood, and industrial food products with high protein content. The reaction of BAs with nitrites available in certain meat products forms nitrosoamine, a carcinogenic compound. Hence BAs are in general considered to be a food hazard and monitoring the level of BAs in food samples becomes crucial as their high concentrations may lead to health problems. This review offers an overview of the available chemical and electrochemical methods that are typically used for the sensing of BAs in food samples. Certain compounds are known to selectively interact with BAs via chemical or non-covalent interactions and these interactions are often accompanied by fluorescence or visible color changes (sometimes visual detection) that could be monitored/assessed using a fluorescence spectrophotometer or UV-vis spectrophotometer (colorimetric methods). The colorimetric methods are limited by sensitivity and selectivity as they are based on straight-forward chemical reactions. In the case of electrochemical sensing of BAs, mediators are often used which undergo oxidation/reduction to produce intermediates that could interact with BAs accompanied by changes in their electrochemical potential. Overall, this review summarizes the available chemical and electrochemical strategies towards the sensing of BAs with a discussion on further prospects.

Optimal route of gold nanoclusters administration in mice targeting Parkinson’s disease

Aim: To explore the optimal route of gold nanoclusters (AuNCs) administration in mice targeting Parkinson’s disease. Materials & methods: Assessing the pharmacokinetic and bioavailability of AuNCs in mice administrated following intravenous, intraperitoneal, gavage and intranasal injection. Investigating the biodistribution of AuNCs in mice by atomic absorption spectrometry and transmission electron microscope. Toxicity assessments of AuNCs were carried out both in cells and in mice. Results: Administration of AuNCs via intraperitoneal injection showed the greatest bioavailability and the longest residence in brain. AuNCs could penetrate blood–brain barrier and be excreted mainly through kidney. No obvious toxicity of AuNCs found in cells and in mice. Conclusion: The optimal route of AuNCs administration in mice targeting Parkinson’s disease is intraperitoneal administration.

A novel gold-nanocluster-based fluorescent sensor for detection of sodium 2-mercaptoethanesulfonate

Gold nanoclusters (Au NCs) are widely used in various types of detections due to their unique fluorescence properties. However, there are rare reports on enhanced fluorescence sensors for drug molecules. Here, we report a novel strategy for detection of sodium 2-mercaptoethanesulfonate (MES) by using a fluorescence-enhanced histidine stabilized Au NCs (His-Au NCs) probe. This fluorescence probe showed excellent selectivity and sensitivity towards MES. Furthermore, we have demonstrated that the fluorescence enhancement of His-Au NCs was attributed to ligand exchange with MES by Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The feasibility of practical applications of this probe was further investigated by sensing the MES content in Mesna injection (Uromitexan).

Independent spectral characteristics of functionalized silver nanoparticles for colorimetric assay of arginine and spermine in biofluids

A colorimetric assay for selective and sensitive detection of arginine and spermine using 6-ATT-AgNPs as a probe.