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In this contribution, we have developed a rapid method for the highly selective detection of mercury ions (Hg 2+ ) using citrate-stabilized triangular silver nanoplates (AgNPs). The colorimetric sensor strategy is based on the aggregation of Hg 2+ -coated AgNPs with the assistance of two amino groups of lysine, resulting in a color change of AgNP solution from blue to mauve or gray. The sensor enables the analysis of Hg 2+ with a minimum detectable concentration that corresponds to 50 nM. Meanwhile, the strategy offers excellent selectivity toward Hg 2+ against other cations. The validation of this method is carried out by analysis of Hg 2+ in tap water with satisfying recoveries over 91.35–106%. [ABSTRACT FROM AUTHOR]

In this study, a simple and highly sensitive colorimetric assay of H 2 O 2 using triangular Ag nanoplates has been carried out. In the presence of H 2 O 2 , the Ag nanoplates are etched from triangle to round, which leads to the vanishment of the surface plasmon resonance (SPR) absorption at 400 nm and significant decrease the absorbance of the band at 670 nm. The color change of the reaction system from the initial blue to mauve can be observed. This proposed method can determine H 2 O 2 with a dynamic range of 50 nM to 1 μM and a low detection limit of 1.36 nM. The high sensitivity of the triangular nanoplates can be ascribed to highly reactive edges/tips, and strongly tip sharpness and aspect ratio dependent SPR absorption of the triangular nanostructure. This sensing system is further extended to the detection of glucose by H 2 O 2 generated from the enzymatic oxidation of glucose, and thus holds great promises in clinical applications. [ABSTRACT FROM AUTHOR]

Abstract: A one-step electrochemical sensor for sensing of potassium ion (K+) based on the conformational change of a single stranded DNA (ssDNA) with G-rich sequence was presented. The introduction of K+ induced folding of the aptamer, and the Fc moiety approached the electrode surface to produce measurable electrochemical signals. The aptasensor had a lower detection limit at 0.1nM, which was an excellent sensitivity compared with other methods for K+ detection. The proposed approach showed high selectivity and minimized the nonspecific adsorption, so that it was used for the detection of target K+ in the human serum sample. [Copyright &y& Elsevier]

We have proposed a colorimetric sensing assay exploiting the formation of gold amalgamation, combining with Hg 2+ mediated the growth of gold nanoparticles (AuNPs) for rapid detecting Hg 2+ ions with highly sensitivity and selectivity. In our developed approach, Hg 2+ is reduced to elemental mercury by citrate-capped AuNPs, forming gold amalgamation on the surface of AuNPs. AuNP-Hg 2+ interaction modulates the growth of AuNPs which is formed in the HAuCl 4 /NH 2 OH reaction. The rate of AuNP growth is highly dependent on the target concentration. AuNPs with low Hg coverage grow into spherical AuNPs with slow growth rate, which generates red-colored solutions. Whereas, AuNPs with high Hg coverage accelerate the growth of spherical AuNPs with a larger particle size, which generates blue colored solutions. At higher concentration, however, the growth rate of AuNPs begins to decrease. As the concentration of Hg 2+ increases till the saturation of Hg onto the surface of AuNPs, the growth of the AuNPs is inhibited due to full coverage of Hg on the AuNP surface. On the basis of this principle, Hg 2+ can be well determined ranging from 0.5 to 10 nM with a 0.26 nM of the detection limit. [ABSTRACT FROM AUTHOR]

Adding preservatives to cosmetics have raised many concerns about health issues. Here, we propose a fluorescence sensor array for preservative discrimination based on two types of CsPbBr 3 nanocrystals (NCs) modified with two different thiol compounds (i.e., 6-mercapto-1-hexanol (6-MCH) and dithiothreitol (DTT)). The redox reaction between the sulphydryl of 6-MCH and DTT and the carbon oxygen double bonds of preservatives will enhance the fluorescence intensity, which is due to the depletion of superficially decorated DTT and 6-MCH at CsPbBr 3. By manipulating this mechanism, different preservatives generate unique fluorescence fingerprint responses through the diverse interactions between targets and two CsPbBr 3 NCs. Thus, two types of preservatives, including four formaldehyde releasers and three parabens, were well distinguished at low concentration using linear discriminant analysis (LDA) by this sensor array. Remarkably, preservative identification in hand cream further proves the array's practical applicability in complex environment. • We propose a fluorescence sensor array for preservative discrimination based on sulphydryl-functionalized CsPbBr 3 NCs. • The redox reaction between the sulphydryl and the C O of preservatives enhance the fluorescence intensity. • Unique fluorescence fingerprints can be differentiated using linear discriminant analysis • Two types of preservatives, including 4 formaldehyde releasers and 3 parabens, were distinguished at low concentration. [ABSTRACT FROM AUTHOR]

We present here a simple and sensitive sensing strategy for thrombin in buffer solution and human serum samples. The key features of this assay lie in target binding-induced DNA hybridization and the formation of gold nanoparticle (AuNP) aggregation. In the presence of thrombin, the binding of the two DNA strands to the same target triggers the hybridization between the complementary sequences of the two DNA strands. The hybridization is able to pull a few AuNPs together to form oligomers. A linear dependence between the absorbance and target thrombin concentration is obtained under optimal conditions in the range from 10 nM–5 μM with a detection limit (LOD) of 7.5 nM estimated at the 3S blank level. Moreover, this method is successfully applied to complex serum samples without complicated sample pretreatment and sophisticated instruments, a dynamic range (10 nM–5 μM) and a detection limit as low as 9.1 nM is achieved. [ABSTRACT FROM AUTHOR]

Mercury ion (Hg 2+ ) has been recognized as one of the most hazardous metal pollutants that can cause deleterious effects on human health and the environment even at low concentrations. Therefore, monitoring of Hg 2+ levels in water is very important in terms of waste management, environmental analysis, toxicology, water safety, and water quality. Here, we provide a highly sensitive and selective colorimetric assay to detect Hg 2+ in aqueous solution using iodide responsive core-shell Cu@Au nanoparticles (Cu@Au NPs). Iodide can induce an appreciable color change of the Cu@Au NP solution from gray to red by transforming the interconnected, irregularly shaped nanoparticles to the single, separated, and nearly spherical ones. In the presence of Hg 2+ , the formation of Cu@Au-Hg nanoalloys can protect the Cu@Au NPs from absorbing more iodide in the solution, the solution color turns pale red. When Hg absorbed on the surface of Cu@Au NPs reaches saturation, Hg prevents iodide from reacting with Cu@Au NPs, thus the solution color remains gray. This method exhibits a wide response range from 0.1 nM to 70 nM, and the detection limit (LOD) of 0.037 nM is obtained. Besides, our Cu@Au NPs-based colorimetric sensor exhibits excellent selectivity for Hg 2+ . [ABSTRACT FROM AUTHOR]

We have developed aptamer-functionalized gold nanoparticles (AuNPs) for the rapid, selective, and sensitive detection of Ag + in aqueous solution. Two DNA strands are designed to functionalized on the surface of AuNPs through Au S bond. In the presence of Ag + , aptamer1 hybridizes with the partially complementary aptamer2 with the aid of C Ag + C bindings, which could lead to different degrees of AuNP aggregation. This process is accompanied by a color change from red to bluish-purple as observed by naked eyes. This colorimetric sensor is shown to detect the presence of as low as a 0.236 nM concentration of Ag + . Importantly, it could be applied to complex samples without complicated sample pretreatment and sophisticated instruments. [ABSTRACT FROM AUTHOR]

In this work, we report an ultrasensitive colorimetric sensing strategy for Cu 2+ based on the Cu 2+ catalyzed TMB-H 2 O 2 reaction, and the signal amplification induced by aptamer-K + -Cu 2+ complex. It is demonstrated that Cu 2+ exhibits an intrinsic peroxidase-like catalytic activity. Thus, we utilize the catalytic activity of Cu 2+ to TMB-H 2 O 2 reaction for direct colorimetric visualization of Cu 2+ for the first time. The limit of detection (LOD) is 2.6 μM. To further improve the sensitivity of Cu 2+ detection, we utilized G-quadruplex-Cu 2+ metalloenzyme complex formed by K + , G-rich DNA, and Cu 2+ to amplify colorimetric signal of TMB-H 2 O 2 reaction. The LOD is as low as 0.076 μM, which is 34-fold lower than that of only Cu 2+ -catalyzed TMB-H 2 O 2 system (2.6 μM). The LOD shows excellent potential for monitoring ultralow levels of Cu 2+ in water samples. [ABSTRACT FROM AUTHOR]

An ultrasensitive colorimetric assay for Hg 2+ detection was presented based on synergistic catalytic effect of gold nanoparticles (AuNPs) and Hg. The AuNPs could catalyze the reduction of Hg 2+ by surface-capping citrate. The effect of Hg 2+ uptake implied amalgam formation and increased the surface area of AuNPs, leading to remarkable catalytic amplification of the peroxidase-like activity of AuNPs. On the basis of this effect, 3,3′,5,5′-tetramethylbenzidine (TMB) as colorimetric probes could be catalyzed into a black blue product in the presence of H 2 O 2 . The detection limit of the colorimetric assay for Hg 2+ is 0.1 nM. Furthermore, the detection limit of Hg 2+ in river water samples and tap water samples are 0.66 nM, and 0.43 nM, respectively. The results are far below the World Health Organization (WHO) permissible limit (30 nM). The assay is highly sensitive, specific, and able to detect Hg 2+ rapidly without requiring sophisticated equipment. In addition, our strategy could also be used as a promising and convenient approach for detection of the target in environmental protection. [ABSTRACT FROM AUTHOR]

Organophosphorus pesticides (OPs) are widely used in pest control. The residual OPs can cause pollution to the environment and harm to the human body. Although OPs can inhibit the activity of acetylcholinesterase (AChE) and lead to neurological diseases, it also provides enlightenment for the development of a simple and sensitive method for the detection of OPs. Herein, we report a colorimetric sensor array using nanozymes (Fe-N-C nanozymes and Cu-N-C nanozymes) combined with natural enzymes to discriminate eight OPs (Iprobenfos (Ipr), Diazinon (Dia), Crotoxyphos (Cro), Bromophos ethyl (Bro), Dipterex (Dip), Chlorpyrifos methyl (Chl), Ethion (Eth), and Omethoate (Ome)) through a cascade reaction system. Surprisingly, eight OPs were successfully identified in tap water at 1 ng mL−1. • We report a colorimetric sensor array using two nanozymes as sensing elements to discriminate organophosphorus pesticides. • Cu-N-C nanozymes show better peroxidase activity than Fe-N-C nanozymes. • Eight OPs were successfully identified in tap water at 1 ng mL−1. • This method opens a paradigm for the development of colorimetric sensor arrays based on nanozymes. [ABSTRACT FROM AUTHOR]

Flavonoids are closely related to human health. The identification and determination of flavonoids is an important and difficult issue. In view of this, this work puts forward a colorimetric sensing array for flavonoid discrimination based on gold nanoparticle (AuNP) aggregation. Two substances (acetylthiocholine iodide (Atc) and S-propionylthiocholine iodide (Ptc)) are hydrolyzed to choline (Chi) under the action of acetylcholinesterase (AcChE). Choline can agglomerate AuNPs by forming Au S bond with its own sulfhydryl functional group. The presence of flavonoids inhibits the AcChE activity, resulting in the formation of different amounts of Chi and different degrees of AuNP aggregation. Controlled by Atc and Ptc as array's receptors, the five flavonoids, including proanthocyanidin (Pro), naringenin (Nar), quercetin (que), flavone (Fla), and curcumin (Cur), were differentiated through their unique colorimetric "fingerprint" pattern-based recognition with the aid of linear discriminant analysis (LDA). The assay is validated under phosphate buffered saline (PBS) buffer conditions as well as in human serum. In addition, identification for diverse concentrations of single flavonoid and different binary and ternary mixtures of flavonoids were also demonstrated. • The identification and determination of flavonoids is an important and difficult issue. • A colorimetric sensor array for flavonoid discrimination based on gold nanoparticle aggregation is developed. • The presence of flavonoids inhibits the AcChE activity, resulting in different degrees of AuNP aggregation. • Identification for diverse concentrations of single flavonoid and flavonoid mixtures were demonstrated. [ABSTRACT FROM AUTHOR]

• We developed an electrochemical sensor based on T-Hg-T aptamer and exonuclease III. to detect Hg2+ concentration. • We use exonuclease III to cleave dsDNA into ssDNA and 5′ -P single mononucleotides. • A good linear relationship between differential pulse voltammetry current and Hg2+ concentrations (1 pM-1 μM) was obtained. • The detection limit of Hg2+ is as low as 0.2182 pM. Mercury ion, as a kind of toxic ion, seriously endangers human health and ecological environment. It is necessary to establish an accurate and sensitive method for detecting Hg2+. In our work, we develop an electrochemical sensor for Hg2+ detection based on thymine-Hg2+-thymine (T-Hg2+-T) coordination. The cleavage of the double-stranded DNA with T-Hg2+-T pairs catalyzed by Exonuclease III (Exo III) is prompted to happen upon binding target Hg2+. [Ru(NH 3) 6 ]3+, which can be electrostatically adsorbed on the negatively charged DNA backbone, was used to convert the electronic signal. A wide linear range (1 pM-1 μM) was obtained with a detection limit of 0.22 pM, which meets the requirements of environmental sample analysis. In addition, the sensor also shows excellent selectivity for Hg2+ detection in the presence of other high-level interfering substances. More importantly, the electrochemical sensor could successfully detect Hg2+ in river water samples, demonstrating its promising potential for detecting Hg2+ in the real world. [ABSTRACT FROM AUTHOR]

• A colorimetric sensor array consists of 3 lanthanide ions as receptors and EBT as probes. • The complexes of EBT and lanthanide ions induce a color change from blue to pink. • Distinct colorimetric variations as "fingerprints" were obtained , and then identified by LDA. • The sensor array can differentiate 5 antioxidants at seven concentrations. A colorimetric sensor array consisting of three lanthanide ions (Eu3+, La3+, and Sm3+) as sensor elements and Eriochrome Black T (EBT) as signal readout was designed. In the presence of lanthanide ions, EBT and lanthanide ions form binary complexes, producing a color change from blue to pink. Upon the addition of antioxidants, the sensor array exhibits cross-reactive responses to antioxidants, the varying color and absorbance changes from the competitive binding from EBT and antioxidants to lanthanide ions were observed. Distinct colorimetric response variations as "fingerprints" were obtained on the sensor array, and then identified through linear discriminant analysis (LDA). LDA illustrates that the sensor array could differentiate five antioxidants (quinolinic acid (QA), 2,3-Pyridinedicarboxylic acid (PA), tannic acid (TCA), tartaric acid (TA), and gallic acid (GA)) at seven concentrations (5, 10, 50, 100, 150, 200, and 250 nM). This demonstrates the potential utility of the sensor array for diagnostic and food monitoring applications. [ABSTRACT FROM AUTHOR]

• We propose a simple but sensitive colorimetric method for the detection of P 2 O 7 4−and PPase. • By counting the IOD of red dots in the dark-field images, P2O74− concentration can be determined. • The linear range of P2O74−concentrations (0.1 nM - 10 mM) and a LOD (0.0324 nM) were obtained. We propose a sensitive colorimetric method for the detection of P 2 O 7 4− and pyrophosphatase (PPase). Without Na 4 P 2 O 7 and PPase, under the catalysis of gold nanoparticles (AuNPs), Cu(II) can be reduced to Cu by nicotinamide adenine dinucleotide (NADH), leading to the Cu-coating onto the surfaces of AuNPs, accompanied by the color change from green to red under the dark-field microscope observation. While in the presence of Na 4 P 2 O 7 , the formation of Au@Cu NPs is suppressed due to the strong complexation reaction between Cu(II) and Na 4 P 2 O 7. Thus, the NPs exhibit uniform green color in the dark-field image. By quantitatively counting the integrated optical density (IOD) of red dots in the dark-field images, P 2 O 7 4− concentration can be accurately determined. A linear logarithmic dependence on P 2 O 7 4− concentrations from 0.1 nM to 10 mM with a limit of detection (LOD) of 0.0324 nM was obtained. The addition of PPase to the Na 4 P 2 O 7 -triggered dispersed AuNPs restores the formation of Au@Cu NPs owing to the hydrolysis of Na 4 P 2 O 7 into sodium phosphate under the catalysis of PPase, resulting in reliable quantification of color change of NPs from red to green in the dark-field images. The LOD is as low as 0.0007 U/mL with a linear dynamic range of 0.005–10 U/mL. [ABSTRACT FROM AUTHOR]