Colorimetric sensors and nanoprobes for characterizing antioxidant and energetic substances

Development of a dual-sensing colorimetric probe for total antioxidant capacity measurement using iron(III)-o-phenanthroline reagent

In this study, a dual-mode sensing system was developed for the determination of total antioxidant capacity (TAC) using the Fe(III)-phenanthroline (Fe(III)-phen) reagent. The first detection mechanism of the system is based on the reduction of the Fe(III)-phen reagent by antioxidants, leading to the formation of the orange-red Fe(II)-phen chelate, which is quantified by the absorbance change at 510 nm. The second mechanism exploits the oxidase-like activity of the Fe(III)-phen complex. This complex generates superoxide anion radicals that oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue-colored oxidized TMB (ox-TMB) charge-transfer complex. In the presence of antioxidants, this reaction is inhibited, resulting in a decrease in ox-TMB formation, and the absorbance change at 652 nm correlates with the TAC of the tested sample. The proposed system was successfully applied to standard antioxidants, synthetic antioxidant mixtures, and real food extracts, demonstrating its applicability and sensitivity for TAC analysis. The linear equation of the calibration graphs obtained for different trolox (TR) concentrations were found to be A510 = 0.0221CTR + 0.0223 (A: absorbance and C: concentration in μM) and ΔA = 0.0301CTR + 0.0583 (ΔA: the difference of absorbance resulting from decreasing ox-TMB formation in the presence of TR, and C: concentration in μM) for the reduction-based Fe(III)-phen method and the TMB-based Fe(III)-phen method, respectively. The limits of detection (LOD) for the reduction based Fe(III)-phen method and the TMB-based Fe(III)-phen method were found to be 0.45 and 0.87 μM, respectively, for trolox. The LOD was calculated using the equation; LOD = 3 sbl/m (sbl: standard deviation of a blank, m: slope of the calibration line). This study presents an innovative approach by utilizing the same probe, Fe(III)-phen, through two distinct mechanisms for the simple, rapid, and sensitive determination of TAC.

"All-in-a-tube" detection of RDX and TNT: old silver mirror reaction revived for nitro-explosive quantification

Inspired by analyte-induced in situ formation/growth of silver nanoparticles (AgNPs), the traditional Tollens' reagent of diamminesilver(I) complex cation [Ag(NH3)2]+ was shown to be capable of detecting explosives. Thus, a color test based on in situ formation of AgNPs was developed for 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT). The resultant yellow-colored AgNPs were characterized using UV-visible spectrophotometry, scanning transmission electron microscopy, and dynamic light scattering measurements. The system displays turn-on absorbance behavior with RDX and TNT, yielding detection limits of 50.3 and 67.2 nmol L-1, respectively. The assay could distinguish between RDX and TNT using a simple extraction-based recovery procedure. Good recoveries for RDX and TNT were obtained from real (Composite B, Composite A5, and Octol) and synthetically prepared formulations. Method validation was performed by statistically comparing the analytical results obtained by the reference liquid chromatography-tandem mass spectrometric method applied to RDX standards and RDX-contaminated soil samples. As a novelty of this system, direct spectrophotometric detection of RDX through its decomposition product, formaldehyde, was successfully performed for the first time. Compared with the widely used indirect spectrophotometric methods based on nitrite formation from RDX degradation, the system is superior in that it does not require pre-hydrolysis of RDX and does not respond to 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX). It is also noteworthy that the system responds to TNT in a way that constitutes an innovative alternative to the existing mechanism of Meisenheimer/Janowsky complex formation in the literature.

Using Agaricus bisporus crude extract in distance based 3D microfluidic paper-based analytical device and spectrophotometric analytical procedures for thiols determination

Novel and simple spectrophotometric and distance based procedures for thiols (L-cysteine, N-acetylcysteine, and glutathione) determination in biological fluids and pharmaceuticals have been proposed based on their inhibitory action on the oxidation of catechol in the presence of Agaricus bisporus crude extract (ABE). The influence of L-glycine, L-alanine, L-proline, L-methionine, L-cystine, ascorbic acid, uric acid, and bilirubin on the thiol determination has been investigated. Uric acid, bilirubin, L-cystine (oxidized thiol), and L-amino acids do not interfere with the determination. The interference of ascorbic acid up to 350 mg/L is eliminated by using Cucumis sativus crude extract (CSE) with ascorbate oxidase activity. Distance based microfluidic paper-based analytical device (DμPAD) has been developed using origami paper device approach and ABE-catechol-3-methyl-2-benzothiazolinone hydrazone (MBTH) system. DμPAD has the 3D structure of three layers: CSE microzone layer, ABE microzone layer, and chemometer layer (catechol + MBTH). This structure allows sequential sample treatment (ascorbic acid oxidation by CSE) and the following introduction of treated sample to ABE and its substrate to perform ABE inhibition. Separate loading of ABE and its substrate allows preventing their interaction prior to sample loading. DμPAD thiol determination is performed by measuring the length of uncolored flow channel, which allows very simple thiol determination and enables complete integration of analytical procedure steps: sample treatment and enzymatic determination with visual signal output. The analytical ranges are (0.3-2.5)∙10-4 M and (1.1-10.0)∙10-4 M, the recoveries are 80.5-126.7 % and 92.0-112.0 %, the RSD values are 1.6-19.0 % and 2.7-10.8 %, for spectrophotometric and DμPAD procedures, respectively. Both easy-to-use procedures have been successfully applied to the determination of total thiol content (all free sulfhydryl groups) in synthetic urine and N-acetylcysteine in a pharmaceutical sample. The values found with DμPAD and spectrophotometric procedures are in good agreement with values obtained using Ellman's reagent.

Morphology-dependent nanoplasmonic assay: a powerful signaling platform for multiplexed total antioxidant capacity analysis

Assessing the total antioxidant capacity (TAC) in biological samples, such as saliva, is essential for health monitoring and disease prevention. TAC plays a critical role in protecting cells from damage caused by free radicals and oxidative stress, which are associated with various conditions, including cancer, cardiovascular diseases, and aging. Key antioxidants, including ascorbic acid (AA), cysteine (CYS), glutathione (GSH), and uric acid (UA), significantly contribute to this protective effect, with salivary levels of these antioxidants reflecting their concentrations in the bloodstream. Therefore, there is a strong demand for a robust, non-toxic colorimetric sensor that can effectively monitor these antioxidants using an innovative approach. This study introduces a multi-colorimetric probe capable of generating high-resolution, naked-eye-detectable color readouts for evaluating salivary TAC. The probe utilizes the morphology-dependent properties of plasmonic nanostructures as recently developed colorimetric sensors, enabling precise and efficient analysis of salivary antioxidants. The assessment of antioxidants was conducted using the probe in combination with pattern recognition analysis for accurate identification and regression analysis for quantification. The probe exhibited linear responses to pure antioxidants and TAC over a broad concentration range: 3.1-60.0, 2.6-60.0, 1.2-20.0, 0.8-20.0, and 0.7-14.0 μmol L-1, with detection limits of 1.1, 0.9, 0.4, 0.3, and 0.2 μmol L-1 for AA, CYS, GSH, UA, and TAC-mixture, respectively. Moreover, performance metrics highlight the robustness and efficacy of the probe in detecting and quantifying antioxidant levels in saliva samples. The efficacy of the developed multi-colorimetric probe was rigorously validated through the analysis of real saliva samples for on-site TAC monitoring. This rapid, cost-effective, user-friendly, non-toxic, and non-invasive method allows for a comprehensive analysis of both individual and total antioxidants, making it highly applicable for health monitoring and disease prevention. Additionally, the probe generates unique response profiles based on varying ratios of endogenous antioxidants, enabling precise TAC quantification in saliva-an essential factor for clinical diagnostics.

Discriminating Analysis of Metal Ions via Multivariate Curve Resolution-Alternating Least Squares Applied to Silver Nanoparticle Sensor

Heavy metals are life-threatening pollutions because of their great toxicity, long-term persistence in nature and their bioaccumulation in living organisms. In this work, we performed multivariate curve resolution-alternating least squares analysis of UV-Vis raw spectra received by a colorimetric sensor constructed on mercaptoundecanoic acid functionalized silver nanoparticles (AgNPs@11MUA) to detect Cd2+, Cu2+, Mn2+, Ni2+, and Zn2+ in water. This combined approach allowed the rapid identification and quantification of multiple heavy metals and showed adequate sensitivity and selectivity, thus representing a promising analytical and computational method for both laboratory and field applications such as environmental safety and public health monitoring.

Analytical Methods for Assessing Thiol Antioxidants in Biological Fluids: A Review

Redox metabolism is an integral part of the glutathione system, encompassing reduced and oxidized glutathione, hydrogen peroxide, and associated enzymes. This core process orchestrates a network of thiol antioxidants like thioredoxins and peroxiredoxins, alongside critical thiol-containing proteins such as mercaptoalbumin. Modifications to thiol-containing proteins, including oxidation and glutathionylation, regulate cellular signaling influencing gene activities in inflammation and carcinogenesis. Analyzing thiol antioxidants, especially glutathione, in biological fluids offers insights into pathological conditions. This review discusses the analytical methods for biothiol determination, mainly in blood plasma. The study includes all key methodological aspects of spectroscopy, chromatography, electrochemistry, and mass spectrometry, highlighting their principles, benefits, limitations, and recent advancements that were not included in previously published reviews. Sample preparation and factors affecting thiol antioxidant measurements are discussed. The review reveals that the choice of analytical procedures should be based on the specific requirements of the research. Spectrophotometric methods are simple and cost-effective but may need more specificity. Chromatographic techniques have excellent separation capabilities but require longer analysis times. Electrochemical methods enable real-time monitoring but have disadvantages such as interference. Mass spectrometry-based approaches have high sensitivity and selectivity but require sophisticated instrumentation. Combining multiple techniques can provide comprehensive information on thiol antioxidant levels in biological fluids, enabling clearer insights into their roles in health and disease. This review covers the time span from 2010 to mid-2024, and the data were obtained from the SciFinder® (ACS), Google Scholar (Google), PubMed®, and ScienceDirect (Scopus) databases through a combination search approach using keywords.

Synthesis of fluorometric carbon nano dots(CNDs) for selective sensing of biologically important Fe3+ and Cu2+ metal ions and evaluating their antioxidant capacity

In this research, CNDs were prepared by a green and cost effective method using Cinnamomum Tamala (bay leaf) as carbon sources. TEM, UV, FTIR, ZETA Potential, PL and Fluorescence methods were used to characterize the produced CNDs and the average particle size is 3.42 nm. This research was conducted on the development of fluorescent sensors for various metal ions, including Fe3+, Cu2+, Zn2+, Ni2+, Pb2+, Cr3+, Mg2+, Na+ 1 and Cd2+. The CNDs demonstrated selective sensing of biologically important Fe+ 3 and Cu+ 2 metal ions. The CNDs antioxidant assay was tasked with DPPH• radical scavenging properties. CNDs made from Cinnamomum Tamala had the highest DPPH free radical scavenging activity at 100 mg/L (42.06%) with the IC50 of 130.68 mg/L. The outcome implies that Indian spices are among the best materials for optical metal ion detection and sensing, and they also have therapeutic benefits.

Development of silver nanoparticles based on the method using quince seed mucilage for ascorbic acid determination

INTRODUCTION

Nanoparticles are used in various fields such as chemistry, pharmacy, biotechnology, and food science since they provide higher sensitivity than traditional optical detection methods. Recently, synthesis of nanomaterials using green chemistry has become popular. Many phytochemical components are used in the synthesis of nanoparticles, including vitamins, proteins, polysaccharides, glycosides, essential oils and phenolic compounds.

OBJECTIVE

A novel green nanotechnology-based method using quince seed mucilage (QSM) was designed for the determination of ascorbic acid in pharmaceutical preparations. QSM, a natural polysaccharide, was used as a bioreducing and stabilizing reagent in the proposed silver nanoparticle (SNP)-based method.

METHOD

In the first stage of the developed method, silver(I) is reduced to silver(0) via QSM and spherical, homogeneous SNPs were prepared (QSM-SNPs). In the second stage of the developed method, SNPs nuclei were enlarged with the addition of ascorbic acid. The developed method was validated by performance parameters (linearity, recovery, and precision). Ascorbic acid determination was performed by measuring increase in absorbance at 420 nm.

RESULTS

The limit of detection and limit of quantification for ascorbic acid were, respectively, found to be at 0.27 and 0.90 μM. The QSM-SNP-based method was successfully applied to effervescent tablets containing ascorbic acid. The standards of the excipients frequently used in pharmaceutical preparations did not interfere with the developed method.

CONCLUSION

The developed QSM-SNP-based method satisfies the requirements of green nanotechnology. The developed QSM-SNP-based method is simple, fast, eco-friendly and low-cost.

Analytical Tools and Methods for Explosive Analysis in Forensics: A Critical Review

This review summarizes (i) compositions and types of improvised explosive devices; (ii) the process of collection, extraction and analysis of explosive evidence encountered in explosive and related cases; (iii) inter-comparison of analytical techniques; (iv) the challenges and prospects of explosive detection technology. The highlights of this study include extensive information regarding the National & International standards specified by USEPA, ASTM, and so on, for explosives detection. The holistic development of analytical tools for explosive analysis ranging from conventional methods to advanced analytical tools is also covered in this article. The most important aspect of this review is to make forensic scientists familiar with the challenges during explosive analysis and the steps to avoid them. The problems during analysis can be analyte-based, that is, interferences due to matrix or added molding/stabilizing agents, trace amount of parent explosives in post-blast samples and many more. Others are techniques-based challenges viz. specificity, selectivity, and sensitivity of the technique. Thus, it has become a primary concern to adopt rapid, field deployable, and highly sensitive techniques.

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.

A voltammetric sensor based on a reduced graphene oxide/β-cyclodextrin/silver nanoparticle/polyoxometalate nanocomposite for detecting uric acid and tyrosine

In the present work, an electrochemical sensor based on reduced graphene oxide/β-cyclodextrin/silver nanoparticle/polyoxometalate (RGO-CD-AgNP-POM) was developed for the simultaneous detection of uric acid (UA) and L-tyrosine (L-Tyr). First, an RGO-CD-AgNP-POM nanocomposite was synthesized via a simple photoreduction method and characterized by transmission electron microscopy (TEM), energy dispersive X-ray imaging (EDS), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). As an electrode material, RGO-CD-AgNP-POM showed wide linear ranges (0.5-500 μM for UA, and 1-400 μM for L-Tyr) and relatively low detection limits (0.11 μM for UA, and 0.23 μM for L-Tyr). In addition, the combination of supramolecular recognition from CD and excellent electrochemical performances from RGO, AgNPs and POM was expected to enhance the sensing performances toward UA and L-Tyr in real samples with favorable recovery ranges (99%-104%). This nanocomposite provides a new platform for developing the family of electrode materials.

Fluorescence turn-off sensing of TNT by polyethylenimine capped carbon quantum dots

In recent years, the determination of 2,4,6-trinitrotoluene (TNT) explosive residues in various matrices has attracted great interest from the perspective of national security and public health. Here, a fluorescent polyethylenimine capped carbon quantum dots (PEI-C-dots) probe was synthesized by a microwave-assisted technique using polyethylenimine and citric acid precursors and used to detect TNT. The sensing mechanism of TNT is based on fluorescence quenching as a result of the donor-acceptor interaction between Meisenheimer anion form of TNT and PEI on the PEI-C-dots surface. The fluorescence quantum yield of the synthesized PEI-C-dots was 54% and the detection limit for TNT was 93 μg/L. It was observed that neither the nitramine group (HMX and RDX) explosives with similar structures nor common soil ions and camouflage agents interfered with the determination of TNT. The interference effect of picric acid was eliminated by removing it with a basic anion exchanger before the determination. This nanosensor allows rapid, simple, selective, and sensitive determination of TNT residues in complex matrices and has the potential to be converted into a kit format.

Construction of metal (Mn, Ce, Eu)-containing species in CN nanocomposites with photo-responsive oxidase-mimicking activity for multi-antioxidant discrimination

On the basis of three M-CN nanocomposites with photo-oxidase activity, a colorimetric sensor is proposed for the pattern recognition of antioxidants.

Metal nanoparticles based lab-on-paper for phenolic compounds evaluation with no sample pretreatment. Application to extra virgin olive oil samples

In this work, a low-cost, disposable, and portable lab-on-paper device is proposed to simultaneously quantify total polyphenol content (TPC) and antioxidant capacity (AOC) in 15 min; the assay requires no pre-treatment of the samples. The lab-on-paper device fabrication has been carried out employing a xurography-based benchtop microfabrication technology using low-cost materials as chromatography paper and polymeric sheets. Extra virgin olive oil (EVOO) phenolic compounds' represents a nutritional added value, nevertheless, the high lipidic content hinders their direct and rapid analysis, resulting in an extremely challenging sample. The realized lab-on-paper allows to perform the dual TPC and AOC determination in three simple steps: (i) sample loading, (ii) analytes transport to the analysis spot, and (iii) double colorimetric analysis exploiting the growth of AuNPs and AgNPs on paper mediated by phenolic compounds. Signal acquisition is achieved using a standard digital camera. The dual colorimetric assay is able to detect phenolic compounds in the 25-500 mg L^-1 range with limits of detection ≤6 mg L^-1 and good reproducibility (RSDs ≤11%). Direct analysis of EVOO samples (n = 30) correlated well (r > 0.92) with conventional spectrophotometric methods for TPC and AOC determination.