Sensitive Colorimetric Detection Research Articles

Color-tunable graphene quantum dots via one-step nitrogen-induced intramolecular charge transfer for in vivo/vitro aminotransferase fluorescence sensing

Monitoring aspartate aminotransferase (AST) has been demonstrated to be a sensitive sign of liver dysfunction and an essential method for determining the health status of the living body. The quantitative analysis of AST in vivo/vitro is still challenged by complicated processes, expensive equipment, and/or limited sensitivity. A colorimetric assay using multicolored fluorescent nanomaterials holds great promise in vivo/vitro sensing for visual and highly sensitive disease diagnosis. However, achieving a one-step synthesis of multicolored fluorescence (FL) GQDs probe presents challenges. Herein, we successfully designed novel multicolored GQDs with a high quantum yield (QY) of 60.7 % via a simple nitrogen-induced intramolecular charge transfer (ICT) approach. Leveraging the non-toxic and color-tunable properties of N-GQDs, we developed an innovative N-GQDs-based FL test paper for sensitive colorimetric on-site detection of AST, employing the FL colorimetric method based on the transamination reaction. The FL quenching intensity demonstrated an excellent linear relationship with the concentration of AST within the range of 2.0−60.0 U/L, achieving an impressively low limit of detection (LOD) as low as 0.065 U/L. Moreover, the N-GQDs were utilized for AST in vivo detection and FL imaging in living zebrafish, further showcasing their potential in various applications such as liver disease diagnosis, assessment of myocardial damage, and monitoring of drug and toxic poisonings.

Highly selective and sensitive colorimetric detection of nitrite in drinking water by acetic acid-capped hierarchical flower-like NiO nanosheets structure

Highly selective and sensitive colorimetric detection of nitrite in drinking water by acetic acid-capped hierarchical flower-like NiO nanosheets structure

Integration of a Cas12a-mediated DNAzyme actuator with efficient RNA extraction for ultrasensitive colorimetric detection of viral RNA

Developing highly sensitive and specific on-site tests is imperative to strengthen preparedness against future emerging infectious diseases. Here, we describe the construction of a Cas12a-mediated DNAzyme actuator capable of converting the recognition of a specific DNA sequence into an amplified colorimetric signal. To address viral RNA extraction challenges for on-site applications, we developed a rapid and efficient method capable of lysing the viral particles, preserving the released viral RNA, and concentrating the viral RNA. Integration of the DNAzyme actuator with the viral RNA extraction method and loop-mediated isothermal amplification enables a streamlined colorimetric assay for highly sensitive colorimetric detection of respiratory RNA viruses in gargle and saliva. This assay can detect as few as 83 viral particles/100 μL in gargle and 166 viral particles/100 μL in saliva. The entire assay, from sample processing to visual detection, was completed within 1 h at a single controlled temperature. We validated the assay by detecting SARS-CoV-2 in 207 gargle and saliva samples, achieving a clinical sensitivity of 96.3 % and specificity of 100%. The assay is adaptable for detecting specific nucleic acid sequences in other pathogens and is suitable for resource-limited settings.

Smartphone Motivated Highly Selective and Sensitive Colorimetric Detection of Hg2+ through Limonin Derived Silver Nanoparticles

Smartphone Motivated Highly Selective and Sensitive Colorimetric Detection of Hg2+ through Limonin Derived Silver Nanoparticles

Active site-tuned high peroxidase-like activity nanozyme for on-the-spot detection of saliva total antioxidant capacity using smartphone devices

Metal-Organic Framework (MOF) based nanozymes with clear structure are beneficial for exploration of structural-performance and exhibit broad prospects in improving activity. In this study, the prepared bimetallic Fe3Ni-MOF nanozyme was superior to single metal MOF in the peroxidase-like activity. Subsequently, a derivative nanozyme (Fe3Ni-MOF-Ar) was prepared by pyrolysis using Fe3Ni-MOF as the precursor in argon atomoshere with controlled temperature. The investigated of Fe3Ni-MOF-Ar revealed that the irregular macroporous state and the presence of heterovalent FeIII/FeII sites of Fe3Ni-MOF-Ar enable the retention, exposure, and electronic structure regulation of active sites, promoting the dual mechanism (the generation of •OH and electron transfer mechanism) and significantly increasing the peroxidase-like activity. Fe3Ni-MOF-Ar exhibited a strong affinity for substrate H2O2, which is higher than horseradish peroxidase. Ascorbic acid and cysteine are typical substances of antioxidants. Fe3Ni-MOF-Ar was used for sensitive colorimetric detection of ascorbic acid and cysteine, and the detection limit was as low as 150 and 60 nM. In addition, the smartphone devices was used to detection of antioxidant equivalent ascorbic acid, with a detection range of 0.5–120 μM. Fe3Ni-MOF-Ar nanozyme is feasible for sensitive detection of saliva total antioxidant capacity.

Porphyrin-based covalent organic framework as oxidase mimic for highly sensitive colorimetric detection of pesticides.

A covalent organic framework-based strategy was designedfor label-free colorimetric detection of pesticides. Covalent organic framework-based nanoenzyme with excellent oxidase-like catalytic activity was synthesized. Unlike other artificial enzymes, porphyrin-based covalent organic framework (p-COF) as the oxidase mimic showed highly catalytic chromogenic activity and good affinity toward TMB without the presence of H2O2, which can be used as substitute for peroxidase mimics and H2O2 system in the colorimetric reaction. Based on the fact that the pesticide-aptamer complex can inhibit the oxidase activity of p-COF and reduced the absorbance at 650nm in UV-Vis spectrum, a label-free and facile colorimetric detection of pesticides was designed and fabricated. Under the optimized conditions, the COF-based colorimetric probe for pesticide detection displayed high sensitivity and selectivity. Taking fipronil for example the limit of detection was 2.7ng/mL and the linear range was 5-500,000ng/mL. The strategy was successfully applied to the detection of pesticides with good recovery , which was in accordance with that of HPLC-MS/MS. The COF-based colorimetric detection was free of complicated modification H2O2, which guaranteed the accuracy and reliability of measurements. The COF-based sensing strategy is a potential candidate for the sensitive detection of pesticides of interests.

A paper-based colorimetric sensor using Au/Ag nanocages for sensitive detection of hydrazine in water samples by smartphone

In this work, Au/Ag nanocages have been used as an effective platform for sensitive colorimetric detection of hydrazine. By adding hydrazine together with silver ions to the hollow Au/Ag nanocages, they undergo a morphological transformation to closed nanoboxes. This leads to a noticeable blue shift in the localized surface plasmon resonance (LSPR) peak position and a distinct color change from blue to purple in the solution. The extent of shift in the LSPR peak of the Au/Ag nanocages exhibited a direct correlation with the concentration of hydrazine within the range of 0.1 to 10.0 µM. The limit of detection (LOD) achieved was 0.03 µM, with a relative standard deviation (RSD) of 1.7% at a concentration of 0.5 µM. Furthermore, we developed a paper-based sensor with smartphone readout for hydrazine detection within the range of 0.5 to 10.0 µM, with an LOD of 0.3 µM and an RSD of 3.3% at a concentration of 2.0 µM. The effectiveness of the sensor was successfully demonstrated in the analysis of hydrazine in environmental samples. This is the first time that Au/Ag nanocages are used for simple paper-based assay. With its high sensitivity, low cost, and rapid analysis time, this method offers a promising solution for the quantitative measurement of hydrazine in environmental samples by portable paper-based test strips.

Development of tumor marker detection and tumor treatment based on silver nanozymes

Nanomaterials with intrinsic enzyme activity (nanozymes) have been widely used as artificial enzymes in biomedicine, especially in tumor diagnosis and treatment. Herein, a kind of water-soluble silver nanozyme (Ag@GQD) was developed with a simple method, which showed two enzymatic activities (peroxidase and oxidase-like activity). Based on the excellent catalytic performance of oxidase-like activity, a simple and highly sensitive colorimetric detection strategy for glutathione (GSH) was established. What’s more, after absorbing DOX, Ag/DOX@GQD could realize the combined treatment of reactive oxygen species and chemotherapy. In conclusion, this study provided evidences that Ag@GQD is effective in tumor diagnosis and treatment, which provided new ideas for exploring nanozymes based on the integration of diagnosis and treatment.

A "Pincer" Type of Acridine-Triazole Fluorescent Dye for Iodine Detection by Both 'Naked-Eye' Colorimetric and Fluorometric Modes.

Iodine, primarily in the form of iodide (I-), is the bioavailable form for the thyroid in the human body. Both deficiency and excess intake of iodide can lead to serious health issues, such as thyroid disease. Selecting iodide ions among anions has been a significant challenge for decades due to interference from other anions. In this study, we designed and synthesized a new pincer-type acridine-triazole fluorescent probe (probe 1) with an acridine ring as a spacer and a triazole as a linking arm attached to two naphthol groups. This probe can selectively recognize iodide ions in a mixed solvent of THF/H2O (v/v, 9/1), changing its color from colorless to light yellow, making it suitable for highly sensitive and selective colorimetric and fluorescent detection in water systems. We also synthesized another molecular tweezer-type acridine-triazole fluorescent probe (probe 2) that exhibits uniform detection characteristics for iodide ions in the acetonitrile system. Interestingly, compared to probe 2, probe 1 can be detected by the naked eye due to its circulation effect, providing a simple method for iodine detection. The detection limit of probe 1 is determined to be 10-8 mol·L-1 by spectrometric titration and isothermal titration calorimetry measurements. The binding stoichiometry between probe 1 and iodide ions is calculated to be 1:1 by these methods, and the binding constant is 2 × 105 mol·L-1.

Cu/Zr Metal–Organic Frameworks with High Peroxidase-Like Activity for Sensitive Electrochemical and Colorimetric Dual-Mode Detection of Hydrogen Peroxide Released from Living Cells

Cu/Zr Metal–Organic Frameworks with High Peroxidase-Like Activity for Sensitive Electrochemical and Colorimetric Dual-Mode Detection of Hydrogen Peroxide Released from Living Cells

Ultrafast sensitive colorimetric detection of cyanide based on dissolving AgI on Au-AgI heterodimeric nanoparticles via UV–vis spectroscopy and single nanoparticle imaging

The high toxicity of cyanide and its great variety of uses in industrial processes make it necessary to develop sensitive and selective sensors for its determination in food and environmental samples. However, the developed methods usually require long time and expensive instrument, hindering on-site detection. In this work, novel colorimetric assays for cyanide detection were achieved by using UV–vis spectroscopy and single nanoparticle (NP) imaging technology based on a mechanism wherein cyanide dissolves AgI on Au-AgI heterodimeric NPs by forming Ag(CN)2-. The reaction occurred in less than 1 s, leading to the change from Au-AgI NPs to Au NPs and thus blueshift of localized surface plasmon resonance. The solution color turned to purple, and then pink from blue, while single NPs under darkfield microscopy transformed from red to yellow and green. In UV–vis spectroscopy, the shift of peak wavelength (Δλ) is linear to cyanide concentration with an equation of Δλ=0.8784 Ccyanide-2.4910 over the range of 0–75 µM. Under darkfield microscopy, the linear regression equations were G/R=0.0677 Ccyanide+0.3717 (R2=0.992) with cyanide over the range of 0.2–4.0 μM and G/R=0.2945 Ccyanide+0.4835(R2=0.994) in the range of 4.0–15.0 μM, where G/R is the intensity ratio in green and red channel. The methods were applied for analysis of waters and foods, achieving recovery rates of 97.4–106.3% for UV–vis spectroscopy and 98.6–108.1% for single NP imaging. The techniques offer expeditious, highly discriminating, and on-site capable solutions for cyanide detection, with high practicality.

MOFs@POMs-derived bimetallic oxide Fe2(MoO4)3 nanoparticles for sensitive colorimetric detection of salicylic acid in aspirin.

Acolorimetric sensing method for salicylic acid (SA) was developed by designing and fabricating bimetallic oxide nanozymes. Firstly, by calcinating MIL-100(Fe)@PMo12 (MOFs@POMs) at different temperature, Fe2(MoO4)3-Ts (T = 400℃, 500℃, 600℃, 700℃) nanoparticles (NPs) were successfully prepared. Secondly, by evaluating the peroxidase-like activities, Fe2(MoO4)3-600 NPs shows the best peroxidase-like activity attributed to the Fenton-like effect and the synergistic coupling interaction between Mo and Fe. Finally, based on the specific complexation between SA and Fe3+, a sensitive colorimetric sensor for SA was established, which exhibits superior selectivity and interference with a detection limit of 0.11μM anda linear range of 10 to 100μM, the lowest LOD for SA to date, to the best of our knowledge.

Enhanced detection of copper residues on citrus surfaces: An innovative copper fenton-catalysed colorimetric approach using creatinine and molybdenum trioxide

Accurate quantification of residual copper from inorganic copper reagents on the surface of citrus fruits is crucial for preventing diseases caused by excessive heavy metal intake. In this study, we developed a rapid colorimetric strategy for copper detection that is enhanced under near-neutral pH conditions, using molybdenum trioxide (MoO3) and creatinine for copper-Fenton catalysis. The introduction of MoO3 enriches the redox reactions of Cu2+/Cu+ within the complex formed by copper ions and creatinine, leading to enhanced copper-Fenton catalytic activity at near-neutral pH. In the presence of H2O2, this system oxidises colourless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxTMB, thereby affording a sensitive colorimetric detection platform for Cu2+. The designed method offers high sensitivity for Cu2+ detection, with a linear range of 0.011.0 μg/mL and a detection limit as low as 0.007 μg/mL. This method was effectively used to analyse copper reagent residues on citrus surfaces, achieving recovery rates of 92.0%115.0%. With its high sensitivity, selectivity, simplicity, and low cost, this colorimetric method shows great potential as an effective approach for determining copper ion levels, particularly for monitoring copper residues in agricultural products.

Fe-Co-Based Metal-Organic Frameworks as Peroxidase Mimics for Sensitive Colorimetric Detection and Efficient Degradation of Aflatoxin B1.

Building multifunctional platforms for integrating the detection and control of hazards has great significance in food safety and environment protection. Herein, bimetallic Fe-Co-based metal-organic frameworks (Fe-Co-MOFs) peroxidase mimics are prepared and applied to develop a bifunctional platform for the synergetic sensitive detection and controllable degradation of aflatoxin B1 (AFB1). On the one hand, Fe-Co-MOFs with excellent peroxidase-like activity are combined with target-induced catalyzed hairpin assembly (CHA) to construct a colorimetric aptasensor for the detection of AFB1. Specifically, the binding of aptamer with AFB1 releases the prelocked Trigger to initiate the CHA cycle between hairpin H2-modified Fe-Co-MOFs and hairpin H1-tethered magnetic nanoparticles to form complexes. After magnetic separation, the colorimetric signal of the supernatant in the presence of TMB and H2O2 is inversely proportional to the target contents. Under optimal conditions, this biosensor enables the analysis of AFB1 with a limit of detection of 6.44 pg/mL, and high selectivity and satisfactory recovery in real samples are obtained. On the other hand, Fe-Co-MOFs with remarkable Fenton-like catalytic degradation performance for organic contaminants are further used for the detoxification of AFB1 after colorimetric detection. The AFB1 is almost completely removed within 120 min. Overall, the introduction of CHA improves the sensing sensitivity; efficient postcolorimetric-detection degradation of AFB1 reduces the secondary contamination and risk to the experimental environment and operators. This strategy is expected to provide ideas for designing other multifunctional platforms to integrate the detection and degradation of various hazards.

Absorption-based colorimetric detection of nickel(II) ion by phase separation of thermoresponsive magnetic nanoparticles under microflow.

Therma-Max™ LSA Streptavidin is a thermoresponsive magnetic nanoparticle (TMNP). It can be introduced conveniently to molecular recognition groups by avidin-biotin interaction. In this study, we demonstrated the detection of nickel(II) ions by the magnetic separation of TMNP induced by their phase transition under microflow. The NTA-tagged TMNP solution mixed with a Ni2+ sample was introduced into a microchannel with a well structure. Moreover, the sample was heated to induce the thermally induced aggregation of TMNP. The Ni-capturing TMNP were trapped in the well by magnetic fields. The supernatant was removed from the outlet, and a dimethylglyoxime (DMG) solution was introduced into the device for colorimetric detection in the well. Because DMG has a higher stability constant with Ni2+, sensitive colorimetric detection of Ni2+ can be achieved in devices where the sample volume, e.g., optical pathlength, is short. To demonstrate the feasibility of the proposed method, a recovery test was conducted using a commercially available cosmetic sample. Therein, complete collection was achieved.

Near-Infrared Responsive Ag@Au Nanoplates with Exceptional Stability for Highly Sensitive Colorimetric and Photothermal Dual-Mode Lateral Flow Immunoassay.

Lateral flow immunoassay (LFIA) has played a vital role in point-of-care (POC) testing on account of its simplicity, rapidity, and low cost. However, the low sensitivity and difficulty of quantitation limit its further development. Sensitive markers with new detection modes are being developed to dramatically improve LFIA's performance. Herein, a ligand-complex approach was proposed to uniformly coat a thin layer of Au onto Ag triangular nanoplates (Ag TNPs) without etching the Ag cores, which not only retain the unique optical properties from Ag TNPs but also acquire the surface stability and biocompatibility of gold. The localized surface plasmon resonance absorption of these Ag@Au TNPs could be finely adjusted from visible (550 nm) to the second near-infrared region (NIR-II) (1100 nm), and even longer, by simply adjusting the ratio between edge length and thickness. Utilizing the Ag@Au TNPs as new markers for LFIA, a highly sensitive colorimetric and photothermal dual-mode detection of the SARS-CoV-2 nucleocapsid protein was achieved with a very low background. The Ag@Au TNPs showed an exceedingly high photothermal conversion efficiency of 61.4% (ca. 2 times higher than that of Au nanorods), endowing the LFIA method with a low photothermal detection limit (40 pg/mL), which was 25-fold lower than that of the colorimetric results. The generality of the method was further verified by the sensitive and accurate analysis of cardiac troponin I (cTnI). This method is robust, reproducible, and highly specific and has been successfully applied to SARS-COV-2 detection in 35 clinical samples with satisfactory results, demonstrating its potential for POC applications.

A dual-ligand lanthanide-based metal-organic framework for highly selective and sensitive colorimetric detection of Fe2.

Accumulation of heavy metals in humans and mammals causes health problems due to their abundance as transition metal ions. Iron (Fe2+) serves significantly in numerous biological processes as a heavy metal ion. In this study, we have designed and prepared a metal-organic framework (MOF) utilizing a one-step solvothermal process, incorporating a dual-ligand combination of terephthalic acid (H2BDC) and α,α',α''-tert-pyridine (TPY) with Eu3+ as the metal node. For this MOF, we termed it Eu-BDC/TPY. Eu-BDC/TPY has superior selectivity over other metal cations. It provides an accurate, sensitive, broad linear range colorimetric method for detecting Fe2+ in a concentration range of 1-50 μM with a modest limit of detection (0.33 μM). Eu-BDC/TPY detects the absence of Fe2+ quickly (within 5 seconds), which is very valuable in practical applications. In addition, the results can be used to create a digital image colorimetric card (DIC) using colorimetric software, enabling instantaneous detection of Fe2+ concentration using a smartphone.

Eu MOF-enhanced FeNCD nanozymes for fluorescence and highly sensitive colorimetric detection of tetracycline.

The constrained enzymatic activity and aggregation challenges encountered by small-sized nanozymes pose obstacles to their practical utility, necessitating a strategy to mitigate aggregation and boost enzymatic catalytic efficiency. In this work, a negatively charged Eu MOF was utilized as the encapsulation matrix, encapsulating the small-sized nanozymes FeNCDs into the Eu MOF to synthesize an FeNCDs@Eu MOF. The dispersibility of the encapsulated FeNCDs was increased, and owing to the negative charge of the FeNCDs@Eu MOF, electrostatic pre-concentration of the positively charged target molecule tetracycline (TC) was facilitated, thereby amplifying the enzymatic catalytic efficiency of the FeNCDs. The response of the FeNCDs to TC increased by nearly 6 times upon encapsulation. The TC detection limit (LOD) of the FeNCDs@Eu MOF-based sensor is as low as 11.63 nM. The incorporation of fluorescence detection expanded the linear range of the sensor, rendering it more suitable for practical sample detection.

Molecularly imprinted sensor based on cascade enzyme system supported by metal-organic framework (UiO-66-NH2) for sensitive colorimetric detection of cholesterol

Cholesterol is a crucial cellular molecule in the human body, and a neutral lipid necessary for maintaining the integrity and fluidity of cell membranes. Additionally, it acts as a precursor for the synthesis of essential substances for living organisms, including steroid hormones, bile acids and vitamins. Nonetheless, cholesterol is not always advantageous, and both excess and deficiency of cholesterol can result in serious diseases. Therefore, maintaining cholesterol at a normal level is of paramount importance for the maintenance of normal cellular activity. In this study, an amino-functionalized metal-organic framework (UiO-66-NH2, abbreviated as U6NH2) was used as a carrier, on the surface of which gold nanoparticles (AuNPs) was embedded and cholesterol oxidase (ChOx) was immobilized, and then cholesterol was employed as a template molecule, followed by the synthesis of molecularly imprinted polymers (MIPs). Remarkably, the obtained U6NH2@AuNPs-ChOx@MIPs can be used to facilitate efficacious and selective detection of blood cholesterol through a facile colorimetric method over a range of 2.9 mM - 6.7 mM with a limit of detection (LOD) = 2.4 mM, while the normal level of blood cholesterol should be less than 5.18 mM. Moreover, the sensing system demonstrates excellent stability and satisfactory selectivity. The constructed cholesterol selective detection system reported in this paper is anticipated to have a crucial impact on bioanalysis.

Flower-like L-Cys-FeNiNPs nanozyme aptasensor for sensitive colorimetric detection of aflatoxin B1

It is vital to create a sensitive and trustworthy sensor for aflatoxin B1 (AFB1) considering the potential hazards this substance poses to the safety of food. Herein, a colorimetric sensor, namely, aptamer-modified flower-like L-cysteine-functionalized FeNi bimetallic nanoparticles (L-Cys-FeNiNPs) with peroxidase-mimicking enzymatic activity, was established for the detection of aflatoxin B1. Interestingly, based on the synergies between FeNi bimetals and the protection and regulation of morphology by L-Cys on FeNiNPs, we successfully synthesized flower-like L-Cys-FeNiNPs, which were employed as outstanding peroxidase-mimic enzymes to oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. Kinetic analysis showed that the flower-like L-Cys-FeNiNPs have an ultralow Michaelis constant (Km) and an ultrahigh affinity for H2O2. Furthermore, based on the peroxidase-mimicking activity of flower-like L-Cys-FeNiNPs, a new colorimetric aptamer sensing strategy was employed for the easy and specific detection of AFB1 with a wide response range (0.12–2 μg/mL) and a low detection limit (36.57 ng/mL). Finally, to verify the practicality of this aptamer detection strategy, we successfully applied it to the detection of AFB1 in actual millet and maize samples.