Rapid and simple colorimetric detection of hydrogen sulfide using an etching-resistant effect on silver nanoprisms.

A fast and sensitive colorimetric paper sensor has been developed using silver nanoprisms (Ag NPRs) with an edge length of ~50 nm for the detection of free H2S gas. We prepared two types of Ag NPRs-coated H2S sensing papers: a multi-zone patterned paper for passive (diffusion mode), and a single-zone patterned paper for pumped mode of H2S gas. The change in color intensity was quantitatively analyzed of Ag NPRs-coated paper after KCl treatment depending on the concentration of H2S gas, from yellow to purplish brown. As a result, Ag NPRs-coated H2S sensing paper showed good sensitivity with a linear range of 1.03 to 32.9 µM H2S, high selectivity, and good reproducibility and stability, together with a fast response time of 1 min. The developed H2S sensing paper was applied to detect the free H2S gas released from three types of garlic including crushed, peeled, and fresh garlic. Therefore, it can be utilized as a simple, fast, and reliable tool for on-site colorimetric detection of free H2S gas for quality control of dietary supplements and exhaled breath analysis.Graphical abstract.

Visual paper-based sensor for the highly sensitive detection of caffeine in food and biological matrix based on CdTe-nano ZnTPyP combined with chemometrics.

Caffeine naturally occurs in tea and cocoa, which is also used as an additive in beverages and has pharmacological effects such as refreshing, antidepressant, and digestion promotion, but excessive caffeine can cause harm to the human body. In this work, based on the specific response between nano zinc 5, 10, 15, 20-tetra(4-pyridyl)-21H-23H-porphine (nano ZnTPyP)-CdTe quantum dots (QDs) and caffeine, combined with chemometrics, a visual paper-based sensor was constructed for rapid and on-site detection of caffeine. The fluorescence of QDs can be quenched by nano ZnTPyP. When caffeine is added to the system, it can pull nano ZnTPyP off the surface of the QDs to achieve fluorescence recovery through electrostatic attraction and nitrogen/zinc coordination. The detection range is 5 × 10-11~3 × 10-9 mol L-1, and the detection limit is 1.53 × 10-11 mol L-1 (R2 = 0.9990) (S/N = 3). The paper-based sensor constructed exhibits good results in real samples, such as tea water, cell culture fluid, newborn bovine serum, and human plasma. Therefore, the sensor is expected to be applied to the rapid instrument-free detection of caffeine in food and biological samples.Graphical abstract.

Identification of Chinese teas by a colorimetric sensor array based on tea polyphenol induced indicator displacement assay.

In this work, we developed an optical colorimetric sensor array for the discrimination of Chinese teas. The sensor array was carefully designed based on tea polyphenol induced indicators displacement assay (IDA), using phenylboronic acids with different substituents as the receptors to polyphenols. The accurate identification for polyphenols with different species or concentrations proved the potential of the sensor array. The sensor array successfully distinguished tea samples within different categories, grades and origins, coupling with PLS-DA. This work offered an efficient and rapid method to distinguish teas and tea-related products. Besides, the assay is supposed to be suitable for the identification of other polyphenol-related natural products.

Fast, Precise, and Reliable Multiplex Detection of Potato Viruses by Loop-Mediated Isothermal Amplification.

Potato is an important staple food crop in both developed and developing countries. However, potato plants are susceptible to several economically important viruses that reduce yields by up to 50% and affect tuber quality. One of the major threats is corky ringspot, which is a tuber necrosis caused by tobacco rattle virus (TRV). The appearance of corky ringspot symptoms on tubers prior to commercialization results in ≈ 45% of the tubers being downgraded in quality and value, while ≈ 55% are declared unsaleable. To improve current disease management practices, we have developed simple diagnostic methods for the reliable detection of TRV without RNA purification, involving minimalized sample handling (mini), subsequent improved colorimetric loop-mediated isothermal amplification (LAMP), and final verification by lateral-flow dipstick (LFD) analysis. Having optimized the mini-LAMP-LFD approach for the sensitive and specific detection of TRV, we confirmed the reliability and robustness of this approach by the simultaneous detection of TRV and other harmful viruses in duplex LAMP reactions. Therefore, our new approach offers breeders, producers, and farmers an inexpensive and efficient new platform for disease management in potato breeding and cultivation.

Validity and reliability of test strips for the measurement of salivary nitrite concentration with and without the use of mouthwash in healthy adults.

The nitrate (NO3-)-nitrite (NO2-)-nitric oxide (NO) pathway has received considerable interest in recent years as a potential target for nutritional interventions designed to increase NO production, and elicit therapeutic effects in humans. In particular, studies have evaluated the effects of supplemental dietary NO3-, which serves as a 'substrate' for this pathway, on numerous different health outcomes. One challenge has been to evaluate compliance with the NO3- interventions. A recent advance in this field has been the development of a non-invasive, simple and rapid method to measure nitrite concentrations in saliva using small test salivary strips. In the present study, ten healthy adults were recruited to a randomised, crossover study and received an acute dose of NO3--rich beetroot juice (BJ) after rinsing their mouth with either water or commercially available antibacterial mouthwash. Salivary NO3- and NO2- concentrations were measured at baseline and up to 5 h after BJ consumption using the gold-standard chemiluminescence and a colorimetric Griess assay. In addition, two salivary test strips (Berkeley Test strips, CA, USA) were used to measure NO2-concentrations at the same time points. Five observers read the strips and inter- and intra-observer reliability was measured. The Bland-Altman method was used to provide a visual representation of the agreement between the methods used to evaluate salivary NO3-/NO2-concentration. Sialin concentrations were measured at baseline and up to 5 h after BJ consumption. BJ elevated salivary NO3- and NO2- concentrations when the mouth was rinsed with water (both P < 0.01), as assessed via both chemiluminescence and Griess methods. Rinsing the mouth with antibacterial mouthwash attenuated markedly the increase in NO2- (P < 0.001), while NO3-concentrations were unaffected (P > 0.05). The Intra-Class Coefficients of Correlation (ICC) showed a high inter- and intra-observer reliability (r > 0.8). A significant positive correlation was found between absolute salivary NO2- concentrations measured by strips and Griess and chemiluminescence methods (rho = 0.83 and 0.77, respectively) and also when expressed as changes in salivary NO2- concentrations (rho = 0.80 and 0.79, respectively). Bland Altman analysis indicated a poor agreement for absolute NO2- concentrations between salivary strips and the chemiluminescence and Griess methods. A small significant negative correlation was found between changes in salivary sialin and salivary NO2- concentrations (r = -0.20, P = 0.04). A non-significant positive correlation was observed between the change in salivary sialin and salivary NO3- concentrations (r = 0.18, P = 0.06). This study suggests that commercially available salivary NO2- test strips provide a reasonable surrogate marker for monitoring changes in salivary NO2- concentrations in humans. However, the strips do not provide accurate estimates of absolute NO2- concentrations.

UIISScan 1.1: A Field portable high-throughput platform tool for biomedical and agricultural applications.

The colorimetric sensing technology has evolved into an essential tool for high-throughput analysis including portability and cost-effectiveness among available biomedical and agricultural screening approach. In this endeavor, the objective of work is to focus on the development of a field-portable instrument based on an Uniform Illumination Imaging System (UIIS), which will facilitate the colorimetric biochemical sensing. The developed field-portable, wavelength independent UIIS has been exploited for (a) rotavirus detection using commercial enzymatic immunoassay based microplate kit; (b) pesticide residue detection and quantification; The proposed system exhibited a good correlation in comparison to another two conventional techniques, i.e., multi-plate reader (r = 0.9991938) and LC-MS/MS (r = 0.998877399) with a short analysis time of 5 min for 95 test samples. Moreover, the feasibility of UIIS system has also been explored as field-portable enzyme-linked immunosorbent assay (ELISA) plate reader. By incorporating the Mahalanobis distance calculation, the advanced algorithm has been investigated and developed to analyze the data. The overall dataset was transformed into a matrix format to give a good correlation with a conventional plate reader, i.e., r = 0.915389612. Internet of things (IoT) enabled decision support system can be exploited by using big data analytics. Finally, test results can be shared with concerned stakeholders and the remote users. Thus, the developed UIIS will help to identify potential public health threats expeditiosly compared to conventional time consuming process of sample submission to the laboratory for analysis.

Digital image colorimetric analysis for evaluating lipid oxidation in oils and its emulsion.

Optical analytical images were captured by a digital camera, and lipid peroxidation was monitored using colorimetric determination. The Image-J method was shown to have comparable accuracy to the conventional titration (American Oil Chemists' Society) and UV-Vis spectroscopic methods. Over the PV range 3-14 meq.O2/kg, a good correlation (R2 = 0.9836) was found between the proposed method and UV-Vis method with an SD of ±0.0339 meq.O2/kg. The range and accuracy of detection were determined from the changes in the Image-J intensity values. At equivalent PV, the limit of detection was 0.175 meq.O2/kg and the limit of quantitation was 0.35 meq.O2/kg. The proposed Image-J application can be used to develop fast and portable devices for monitoring peroxide values. These have potential applications in quality control for small-scale farmers and small and medium enterprises.

A polyamidoamine-mediated competitive colorimetric assay based on gold nanoparticles for determining acid values in edible sunflower seed, corn and extra virgin olive oils.

We synthesized polyamidoamine (PAMAM) dendrimers and citrate-capped gold nanoparticles (AuNPs), and explored the applicability of the PAMAM/AuNP assay in determining total free fatty acid (FFA) contents in edible oils based on a competitive colorimetry, in which the PAMAM-triggered AuNP aggregation was suppressed by FFAs. The generation and concentration of PAMAMs, the chain lengths of FFAs as well as the concentration and pH of the background electrolytes of the assay were optimized. The average acid values of the sunflower seed, corn and extra virgin olive oils determined by PAMAM/AuNP assay were 1.31 ±â€¯0.07, 0.33 ±â€¯0.02 and 1.49 ±â€¯0.07, respectively, which were not significantly different from the corresponding 1.27 ±â€¯0.08, 0.32 ±â€¯0.01 and 1.61 ±â€¯0.06 by the standard nonaqueous titration. Our results suggest that the method is promising in detecting FFAs in edible oils, and implementation of the method expands the technological scope for FFA analysis.

Morphological control of nanoprobe for colorimetric antioxidant detection.

Colloidal metal nanoparticles (NPs) with remarkable localized surface plasmon resonance (LSPR) have found wide use as probes in sensing. The LSPR that employed as the sensing signal is strongly associated with the morphology of nanoprobes. In this work, morphological change of Au nanocage to Au@Ag nanobox and thus the LSPR evolution are well regulated by trace amount of antioxidant, where the mechanism of seed-mediated growth is used as a powerful means in this process. Based on the linear relationship between morphology-induced LSPR evolution and the concentration of antioxidant, a simple, reliable and highly sensitive colorimetric method is developed for antioxidant detection. The detectable range of this method is 0.01-5 µM and 2-20 µM when a UV-vis spectrophotometer and a smartphone are employed as an analyzer, respectively. It has also been successfully applied in the detection of total antioxidants in green tea. This work provides new insights into developing sensitive LSPR-based sensors through precisely manipulating the morphology of nanoprobes.

A sensitive colorimetric aptasensor based on trivalent peroxidase-mimic DNAzyme and magnetic nanoparticles.

In this study, a novel colorimetric aptasensor was prepared by coupling trivalent peroxidase-mimic DNAzyme and magnetic nanoparticles for highly sensitive and selective detection of target proteins. A three G-quadruplex (G4) DNA-hemin complex was employed as the trivalent peroxidase-mimic DNAzyme, in which hemin assisted the G4-DNA to fold into a catalytic conformation and act as an enzyme. The design of the aptasensor includes magnetic nanoparticles (MNPs), complementary DNA (cDNA) modified with biotin, and a label-free single strand DNA (ssDNA) including the aptamer and trivalent peroxidase-mimic DNAzyme. The trivalent DNAzyme, which has the highest catalytic activity among multivalent DNAzymes, catalyzed the H2O2-mediated oxidation of ABTS. The colorless ABTS was oxidized to produce a blue-green product that can be clearly distinguished by the naked eye. The aptamer and trivalent peroxidase-mimic DNAzyme promote the specificity and sensitivity of this detection method, which can be generalized for other targets by simply replacing the corresponding aptamers. To demonstrate the feasible use of the aptasensor for target detection, a well-known tumor biomarker MUC1 was evaluated as the model target. The limits of detection were determined to be 5.08 and 5.60 nM in a linear range of 50-1000 nM in a buffer solution and 10% serum system, respectively. This colorimetric and label-free aptasensor with excellent sensitivity and strong anti-interference ability has potential application in disease diagnoses, prognosis tracking, and therapeutic evaluation.

Modified Sample Preparation Approach for the Determination of the Phenolic and Humic-Like Substances in Natural Organic Materials By the Folin Ciocalteu Method.

A novel modification of the sample preparation procedure for the Folin-Ciocalteu colorimetric assay for the determination of total phenolic compounds in natural solid and semisolid organic materials (e.g., foods, organic solid waste, soils, plant tissues, agricultural residues, manure) is proposed. In this method, the sample is prepared by adding sodium sulfate as a solid diluting agent before homogenization. The method allows for the determination of total phenols (TP) in samples with high solids contents, and it provides good accuracy and reproducibility. Additionally, this method permits analyses of significant amounts of sample, which reduces problems related to heterogeneity. We applied this method to phenols-rich lignocellulosic and humic-like solids and semisolid samples, including rice straw (RS), peat-rich soil (PS), and food waste (FW). The TP concentrations measured with the solid dilution (SD) preparation were substantially higher (increases of 41.4%, 15.5%, and 59.4% in RS, PS and FW, respectively) than those obtained with the traditional method (solids suspended in water). These results showed that the traditional method underestimates the phenolic contents in the studied solids.

Fabrication and response of alpha-hydroxybutyrate sensors for rapid assessment of cardiometabolic disease risk.

Early diagnosis and treatment can prevent or delay progression of early-stage type 2 diabetes and prediabetes. Unfortunately, tests such as hemoglobin A1c (HbA1c)/fasting plasma glucose (FPG) alone fail to diagnose or miscategorize up to 40% of individuals with impaired glucose tolerance (IGT) or frank diabetes based on the rarely utilized oral glucose tolerance test (OGTT). The serum metabolite alpha-hydroxybutyrate (AHB) is increasingly recognized as a reliable IGT and diabetes predictor, and can be measured using liquid chromatography-tandem mass spectrometry. However, to address AHB adoption as a population screening tool, the reliable and low-cost measurement techniques are proposed. A periodate based oxidation was performed for an AHB-based buffer, and both nitroprusside and Raman tests confirmed the formation of a slow-oxidation product. Electrochemical tests of AHB-based buffers using electrodes such as Au-honeycomb, thiol self-assembled monolayers coated Au, 2D material (black-P) coated FTO, (3-aminophenyl) triethoxysilane modified TiO2, were performed. Many of these electrodes exhibited a systematic response when AHB concentration was varied from ~1.0-12.0µg/ml. A colorimetric assay containing a vicinal-diol recognition moiety, additives, and a photoinitiator, exhibited a different color for AHB based buffer. Benesi-Hildebrand analysis indicated the association behavior of boronic acid and AHB. These methods have a potential to be used for rapid point-of-care measurements of AHB that could enhance population-wide diabetes and prediabetes screening strategies.

A Miniaturized On-Chip Colorimeter for Detecting NPK Elements.

Recently, precision agriculture has become a globally attractive topic. As one of the most important factors, the soil nutrients play an important role in estimating the development of precision agriculture. Detecting the content of nitrogen, phosphorus and potassium (NPK) elements more efficiently is one of the key issues. In this paper, a novel chip-level colorimeter was fabricated to detect the NPK elements for the first time. A light source-microchannel photodetector in a sandwich structure was designed to realize on-chip detection. Compared with a commercial colorimeter, all key parts are based on MEMS (Micro-Electro-Mechanical System) technology so that the volume of this on-chip colorimeter can be minimized. Besides, less error and high precision are achieved. The cost of this colorimeter is two orders of magnitude less than that of a commercial one. All these advantages enable a low-cost and high-precision sensing operation in a monitoring network. The colorimeter developed herein has bright prospects for environmental and biological applications.

Zein as biodegradable material for effective delivery of alkaline phosphatase and substrates in biokits and biosensors.

A biodegradable material, zein, is proposed as a reagent delivery platform for biokits and biosensors based on alkaline phosphatase (ALP) activity/inhibition in the presence of phosphatase substrates. The immobilization and release of both the substrate and/or the active ALP, in a biodegradable and low-cost material such as zein, a prolamin from maize, and in combination with glycerol as plasticizer have been investigated. Three zein-based devices are proposed for several applications: (1) inorganic phosphorus estimation in water of different sources (river, lake, coastal water and tap water) with a detection limit of 0.2mg/L - compared to at least 1mg/L required by legislation, (2) estimation of ALP in saliva and (3) chlorpyrifos control in commercial preparations. The single-use kits developed are low cost, easy and fast to manufacture and are stable for at least 20 days at -20°C, so the zein film can preserve and deliver both the enzyme and substrates.

Storing Tooth Segments for Optimal Esthetics.

OBJECTIVE: A fractured whole crown segment can be reattached to its remnant; crowns from extracted teeth may be used as pontics in splinting techniques. We aimed to evaluate the effect of different storage solutions on tooth segment optical properties after different durations. STUDY DESIGN: Sixty central incisor crowns were divided into 6 groups (n = 10); Group 1 was kept dry; Groups 2, 3, 4, 5, and 6 were placed in an isotonic solution, water, milk, saliva, and casein-phosphopeptide-amorphous-calcium-phosphate (CPP-ACP), respectively, for 30 min, 12 h, 1 day, 1 week, and 3 weeks. Color values were measured using a colorimeter. Data were analyzed with Kruskal-Wallis tests, Mann-Whitney U-tests, and Friedman Wilcoxon tests with Bonferroni stepwise corrections (p < 0.05). RESULTS: ΔE* values varied from 0.3 to 15.3 over the 3 week period. Group 1 demonstrated the greatest color changes over all durations; Group 6 exhibited the least. L*, a*, b*, and ΔE* values varied between time periods in all groups; the differences were significant (p < 0.01), except for L* and ΔE* values in Group 2 and a* values in Group 6 (p > 0.01). Comparing ΔE* values, Group 6 was significantly different from the other groups for all durations (p < 0.01), except Group 4. CONCLUSIONS: A CPP-ACP complex solution seems a good choice for tooth fragment storage. Milk and saliva solutions may cause perceptible color changes if tooth fragments are stored for 3 weeks before use.

A FRET-based ratiometric fluorescent aptasensor for rapid and onsite visual detection of ochratoxin A.

A color change observable by the naked eye to indicate the content of an analyte is considered to be the most conceivable way of various sensing protocols. By taking advantage of the Förster resonance energy transfer (FRET) principles, we herein designed a dual-emission ratiometric fluorescent aptasensor for ochratoxin A (OTA) detection via a dual mode of fluorescent sensing and onsite visual screening. Amino group-modified OTA's aptamer was firstly labeled with the green-emitting CdTe quantum dots (gQDs) donor. The red-emitting CdTe QDs (rQDs) which were wrapped in the silica sphere could serve as the reference signal, while the gold nanoparticle (AuNP) acceptors were attached on the silica surface to bind with the thiolated complementary DNA (cDNA). The hybridization reaction between the aptamer and the cDNA brought gQD-AuNP pair close enough, thereby making the FRET occur in the aptasensor fabrication, while the subsequent fluorescence recovery induced by OTA was obtained in the detection procedure. Based on the red background of the wrapped rQDs, the aptasensor in response to increasing OTA displayed a distinguishable color change from red to yellow-green, which could be conveniently readout in solution even by the naked eye. Since the bioconjugations used as the aptasensor can be produced at large scale, this method can be used for in situ, rapid, or high-throughput OTA detection after only an incubation step in a homogeneous mode. We believe that this novel aptasensing strategy provides not only a promising method for OTA detection but also a universal model for detecting diverse targets by changing the corresponding aptamer.

Identification and Characterization of EDTA Test Strip Interfering Substances Using a Digital Color Detector.

BACKGROUND: Rapid test strips for ethylenediaminetetraacetic acid (EDTA) can be used to verify correct specimen types for clinical assays which require, or cannot be performed on, plasma collection tubes containing EDTA anticoagulant. As the test strip reaction chemistry is based on a color change induced by chelation of bismuth from a xylenol orange complex, we hypothesized that any agent capable of chelating bismuth might induce false positive test strip reactivity. The present study was therefore designed to evaluate the potential for test strip interference by chelating agents commonly used in the treatment of trace and heavy metal toxicity. METHODS: A digital color detector mounted on a 3D-printed test strip holder was used to quantitatively assess test strip reactivity and evaluate concentration-response relationships of eight commercially available chelating agents. RESULTS: This approach revealed the following rank-order potency: K2EDTA = Na2EDTA > ethylene glycol tetra-acetic acid (EGTA) > dimercaptosuccinic acid (DMSA) > 2,3-dimercapto-1-propanesulfonic acid (DMPS) > penicillamine (PEN). Both deferoxamine (DEF) and alpha lipoic acid (ALA) were non-reactive at 10 mM concentrations. CONCLUSIONS: These experiments demonstrate that multiple substances can induce EDTA rapid test strip reactivity, but only at concentrations higher than might be expected during therapeutic chelation therapy. These agents are therefore unlikely to cause false positive results in routine clinical laboratory specimens.

Colorimetric sensor array for detection and identification of organophosphorus and carbamate pesticides.

Due to relatively low persistence and high effectiveness for insect and pest eradication, organophosphates (OPs) and carbamates are the two major classes of pesticides that broadly used in agriculture. Hence, the sensitive and selective detection of OPs and carbamates is highly significant. In this current study, a colorimetric sensor array comprising five inexpensive and commercially available thiocholine and H2O2 sensitive indicators for the simultaneous detection and identification of OPs and carbamates is developed. The sensing mechanism of this array is based on the irreversible inhibition capability of OPs and carbamates to the activity of acetylcholinesterase (AChE), preventing production of thiocholine and H2O2 from S-acetylthiocholine and acetylcholine and thus resulting in decreased or no color reactions to thiocholine and H2O2 sensitive indicators. Through recognition patterns and standard statistical methods (i.e., hierarchical clustering analysis and principal component analysis), the as-developed array demonstrates not only discrimination of OPs and carbamates from other kinds of pesticides but, more interestingly, identification of them exactly from each other. Moreover, this array is experimentally confirmed to have high selectivity and sensitivity, good anti-interference capability, and potential applications in real samples for OPs and carbamates.

Quality evaluation of Hypericum ascyron extract by two-dimensional high-performance liquid chromatography coupled with the colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method.

In this paper, a heart-cutting two-dimensional high-performance liquid chromatography coupled with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method was established for controlling the quality of different batches of Hypericum ascyron extract for the first time. In comparison with the common one-dimensional fingerprint, the second-dimensional fingerprint compiled additional spectral data and was hence more informative. The quality of H. ascyron extract was further evaluated by similarity measures and the same results were achieved, the correlation coefficients of the similarity of ten batches of H. ascyron extract were ＞0.99. Furthermore, we also evaluated the quality of the ten batches of H. ascyron extract by antibacterial activity. The result demonstrated that the quality of the ten batches of H. ascyron extract was not significantly different by MTT. Finally, we demonstrated that the second-dimensional fingerprint coupled with the MTT method was a more powerful tool to characterize the quality of samples of batch to batch. Therefore the proposed method could be used to comprehensively conduct the quality control of traditional Chinese medicines.

Tandem measurements of iron and creatinine by cross injection analysis with application to urine from thalassemic patients.

This work presents development of a method for the dual determination of Fe(III) and creatinine using cross injection analysis (CIA). Two CIA platforms connected in series accommodated sample and reagents plugs aspirated via y-direction channels while water was pumped through the x-direction channel toward a flow-through cell of a diode array UV-vis. detector. Iron was detected from the colorimetric reaction between Fe(II) and 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-(3-sulfopropyl)amino) aniline (5-Br-PSAA), with prior reduction of Fe(III) to Fe(II) by ascorbic acid. The Jaffe's reaction was employed for the detection of creatinine. Under the optimal conditions, good linearity ranges were achieved for iron in the range 0.5 to 7 mg L(-1) and creatinine in the range 50 to 800 mg L(-1). The CIA system was applied to spot urine samples from thalassemic patients undergoing iron chelation therapy, and was successfully validated with ICP-OES and batchwise Jaffe's method. Normalization of urinary iron excretion with creatinine is useful for correcting the iron concentration between urine samples due to variation of the collected urine volume.