Colorimetric Detection System Research Articles

Design and optimization of a colorimetric biosensor using functionalized gold nanoparticles and bi-functional linker for agriculture and food industry

This study aims to develop a highly sensitive colorimetric detection system utilizing functionalized gold nanoparticles (f-AuNPs) and bifunctional linkers (BLs) for the detection of pathogens and contaminants in food matrices. The primary objective was to explore and optimize key parameters, including reaction time, system volume and the concentration of bifunctional linkers, in order to enhance the system’s detection capabilities. The core mechanism of the bi-functional linker-based detection system is based on the aggregation of streptavidin-functionalized AuNPs (stAuNPs), which varies in accordance with the concentration of the bifunctional linkers (BLs) and reflects the quantity of effective linkers (EALs) available in the system. The process comprises the binding of the targets and BLs, a reduction in EAL concentration, an increase in the BLs concentration required for the aggregation of the stAuNPs, and a shift in the range exhibiting a visible color change (REVC). In systems without a target, all BLs induce aggregation. In contrast, in systems with a target present, some BLs are bound by the target, reducing EAL concentration and altering the optimal BLs concentration for stAuNP aggregation. The system was shown to be capable of detecting protein in PBS at concentrations as low as 2 nM, as well as Salmonella at 101 CFU/mL. In whole milk, the detection limits were 20 nM for protein and 102 CFU/mL for Salmonella. The principal conclusion is that the BLs-based system provides a robust and adaptable platform for pathogen detection, even in complex food matrices, obviating the need for preprocessing. The findings demonstrate the system’s potential for practical applications in the fields of food safety and agricultural contaminant detection, offering clear visual signals and high sensitivity.

Facile Preparation of Tannic Acid-Gold Nanoparticles for Catalytic and Selective Detection of Mercury(II) and Iron(II) Ions in the Environmental Water Samples and Commercial Iron Supplement.

Tannic acid (TA), a plant-derived polyphenol rich in hydroxyl groups, serves as both a reducing agent and stabilizer for synthesizing gold nanoparticles (TA-AuNPs). This study presents a groundbreaking method that utilizes TA to fabricate TA-AuNPs and develop two distinct colorimetric detection systems for mercury (Hg2+) and iron (Fe2+) ions. The first detection system leverages the interaction between TA-AuNPs and Hg2+ to enhance the peroxidase-like activity of TA-AuNPs, facilitating the production of hydroxyl radicals upon reaction with hydrogen peroxide, which subsequently oxidizes 3,3',5,5'-tetramethylbenzidine (TMB) into a blue-colored product (ox-TMB). The second system capitalizes on TA-AuNPs to catalyze the Fenton reaction between Fe2+ and hydrogen peroxide in the presence of 2, 6-pyridinedicarboxylic acid, boosting the generation of hydroxyl radicals that oxidize TMB into a blue-colored ox-TMB. Absorbance measurements at 650 nm display a linear relationship with Hg2+ concentrations ranging from 0.40 to 0.60 μM (R2 = 0.99) and Fe2+ concentrations from 0.25 to 2.0 μM (R2 = 0.98). The established detection limits for Hg2+ and Fe2+ are 18 nM and 96 nM, respectively. Applications to real-world samples achieved an excellent spiked recovery, spanning 101.6% to 108.0% for Hg2+ and 90.0% to 112.5% for Fe2+, demonstrating the method's superior simplicity, speed, and cost-effectiveness for environmental monitoring of these ions compared to existing techniques.

Copper-doped carbon dots nanozymes for multi-signal specific hydrogen sulfide assay and broad-spectrum antibacterial

The emergence of carbon dots-based nanozymes (CDNEs) has opened a broad horizon for multi-mode analysis and safety antibacterial application. However, the practical applications of CDNEs are currently hindered by unsatisfactory performance and complicated synthetic methodology. In this study, we developed a novel copper-doped CDNEs (Cu-CDNEs) with both excellent fluorescence property and peroxidase-like activity. The Cu-CDNEs can be synthesized easily by pyrolyzing a solid mixture of copper glutamate and ethylenediamine hydrochloride for 5 min. By investigating the inhibition of H2S on the peroxidase-like activity of Cu-CDNEs and the competitive interaction between H2S and 3,3′,5,5′-tetramethylbenzidine with reactive oxygen species, we established a dual-mode analysis system for colorimetric and fluorescent detection of H2S with the limit of detection of 20 nM and 25 nM, respectively. Furthermore, a convenient scanometric analysis mode also was developed and successfully applied for the accurate determination of H2S in actual water samples with recoveries of 96.8 %–107.7 %. Moreover, the designed Cu-CDNEs show good cytocompatibility from MTT results, and demonstrated broad-spectrum antibacterial capacity against Gram-positive/negative bacteria due to the surface positive charge and peroxidase-like activity. This study may provide valuable insights for rational design and broad applications in environmental and biomedical fields using functional nanozymes.

Quantitative analysis of zearalenone in wheat leveraging support vector machine and olfactory visualization technology

Zearalenone (ZEN) is a contaminant found naturally in grains such as wheat that poses a potential threat to human and animal health. This study describes a colorimetric sensor array detection system based on chemically reactive dyes and chemometric algorithms for the determination of ZEN in wheat. Firstly, six chemically responsive dyes were screened to construct a colorimetric sensor array to obtain the response fingerprints of the volatile components of wheat. The RGB differences of the chemically reactive dyes before and after the response were then calculated to obtain the color component data of the image. The maximum information coefficient (MIC) and ReliefF methods were then used to select the best color features. Finally, the Support Vector Machine Regression (SVR) prediction model was developed and validated based on the optimized features on 132 sample sets. The results showed that the SVR model developed on the initial 132 wheat samples had good predictive ability. Its root mean square error (RMSE) on the prediction set was 38.1625 μg∙kg−1 with a correlation coefficient (R) 0.9516. In particular, the SVR model combining 13 color components reduced the RMSE on the prediction set to 30.4484 μg∙kg−1, with an improved R of 0.9695. Olfactory visualization techniques were shown to be effective for the determination of ZEN in wheat. This study is expected to provide a scientifically novel approach for quality stabilization during the storage of wheat or other cereals.

Dual-recognition colorimetric platform based on porous Au@Pt nanozymes for highly sensitive washing-free detection of Staphylococcus aureus.

Adual-recognition strategy is reportedto construct a one-step washing and highly efficient signal-transduction tag system for high-sensitivity colorimetric detection of Staphylococcus aureus (S. aureus). The porous (gold core)@(platinum shell) nanozymes (Au@PtNEs) as the signal labels show highly efficient peroxidase mimetic activity and arerobust. For the sake of simplicity the detection involved the use of a vancomycin-immobilized magnetic bead (MB) and aptamer-functionalized Au@PtNEs for dual-recognition detection in the presence of S. aureus.In addition, we designed a magnetic plate to fit the 96-well microplate to ensure consistent magnetic properties of each well, which can quickly remove unreacted Au@PtNEs and sample matrix while avoiding tedious washing steps. Subsequently, Au@PtNEs catalyze hydrogen peroxide (H2O2) to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) generating a color signal. Finally, the developed Au@PtNEs-based dual-recognition washing-free colorimetric assay displayed a response in the range of S. aureus of 5 × 101-5 × 105 CFU/mL, and the detection limit was 40 CFU/mL within 1.5 h. In addition, S. aureus-fortified samples were analyzed to further evaluate the performance of the proposed method, which yielded average recoveries ranging from 93.66 to 112.44% and coefficients of variation (CVs) within the range 2.72-9.01%. These results furnish a novel horizon for the exploitation of a different mode of recognition and inexpensive enzyme-free assay platforms as an alternative to traditional enzyme-based immunoassays for the detection of other Gram-positive pathogenic bacteria.

Split T7 switch-mediated cell-free protein synthesis system for detecting target nucleic acids

Cell-free protein synthesis (CFPS) reactions can be used to detect nucleic acids. However, most CFPS systems rely on a toehold switch and exhibit the following critical limitations: (i) off-target signals due to leaky translation in the absence of target nucleic acids, (ii) a suboptimal detection limit of approximately 30 nM without pre-amplification, and (iii) labor-intensive screening processes due to sequence constraints for the target nucleic acids. To overcome these shortcomings, we developed a new split T7 switch-mediated CFPS system in which the split T7 promoter was applied to a three-way junction structure to selectively initiate transcription–translation only in the presence of target nucleic acids. Both fluorescence and colorimetric detection systems were constructed by employing different reporter proteins. Notably, we introduced the self-complementation of split fluorescent proteins to streamline preparation of the proposed system, enabling versatile applications. Operation of this one-pot approach under isothermal conditions enabled the detection of target nucleic acids at concentrations as low as 10 pM, representing more than a thousand times improvement over previous toehold switch-based approaches. Furthermore, the proposed system demonstrated high specificity in detecting target nucleic acids and compatibility with various reporter proteins encoded in the expression region. By eliminating issues associated with the previous toehold switch system, our split T7 switch-mediated CFPS system could become a core platform for detecting various target nucleic acids.

Triplex immunomagnetic separation combined with loop-mediated isothermal amplification on a microfluidic chip for simultaneous visual detection of Escherichia coli O157:H7, Salmonella enteritidis and Staphylococcus aureus in milk

Escherichia coli O157:H7, Salmonella enteritidis, and Staphylococcus aureus are widely present in food and can cause serious and large-scale cases of illness worldwide every year. Herein, we developed a triplex immunomagnetic separation (IMS) combined with loop-mediated isothermal amplification (LAMP) on a microfluidic chip (triplex IMS-mLAMP) for the simultaneous detection of these three important foodborne pathogenic bacteria. To optimize the triplex IMS method, the CEs of the three types of IMBs were determined for different particle sizes, amounts and incubation times. Under optimal reaction conditions, the CEs for the three bacteria were between 65.4% and 71.1% in PBS, and between 41.1% and 47.5% in milk, respectively. After triplex IMS, DNA from target bacteria captured by magnetic beads was extracted and subjected to a multiplexed LAMP reaction in a centrifugal microfluidic chip that allowed for the simultaneous detection of up to 8 individual milk samples. The results were judged directly by the color change. The method only detected the three target bacteria and did not show cross-reaction with other bacteria, exhibiting a high level of specificity. Sensitivity experiments confirmed a detection limit of the triplex IMS-mLAMP as low as 1.2 × 102 CFU/mL for E. coli O157:H7 and S. enteritidis, and 2.5 × 102 CFU/mL for S. aureus in milk samples. The overall testing time of the triplex IMS-mLAMP was just 80 min. This is the first report that IMS-mLAMP was used for simultaneous capture and detection of E. coli O157:H7, S. enteritidis, and S. aureus in milk. This cost-effective, easy-to-use, no need for expensive laboratory-based equipment, integrated on-chip colorimetric multi-target detection system opens a novel pathway for rapid diagnostic screening of pathogens in food.

Rapid and highly sensitive colorimetric LAMP assay and integrated device for visual detection of monkeypox virus

BackgroundThe monkeypox virus (MPXV) is a linear double-stranded DNA virus with a large genome that causes tens of thousands of infections and hundreds of deaths in at least 40 countries and regions worldwide. Therefore, timely and accurate diagnostic testing could be an important measure to prevent the ongoing spread of MPXV and widespread epidemics. ResultsHere, we designed multiple sets of primers for the target region of MPXV for loop-mediated isothermal amplification (LAMP) detection and identified the optimal primer set. Then, the specificity in fluorescent LAMP detection was verified using the plasmids containing the target gene, pseudovirus and other DNA/RNA viruses. We also evaluated the sensitivity of the colorimetric LAMP detection system using the plasmid and pseudovirus samples, respectively. Besides, we used monkeypox pseudovirus to simulate real samples for detection. Subsequent to the establishment and introduction of a magnetic beads (MBs)-based nucleic acid extraction technique, an integrated device was developed, characterized by rapidity, high sensitivity, and remarkable specificity. This portable system demonstrated a visual detection limit of 137 copies/mL, achieving sample-to-answer detection within 1 h. SignificanceThe device has the advantages of integration, simplicity, miniaturization, and visualization, which help promote the realization of accurate, rapid, portable, and low-cost testing. Meanwhile, this platform could facilitate efficient, cost-effective and easy-operable point-of-care testing (POCT) in diverse resource-limited settings in addition to the laboratory.

Mobile phone-assisted imprinted nanozyme for bicolor colorimetric visual detection of erythromycin in river water and milk samples

The residues of erythromycin (ERY) may have negative impacts on the ecological environment, health, and food safety. How to detect ERY effectively and visually is a challenging issue. Herein, we synthesized a molecularly imprinted polymer based nanozymes for selective detection of erythromycin (ERY-MIPNs) at neutral pH, and developed a mobile phone-assisted bicolor colorimetric detection system. This system produced a wide range of color changes from blue to pinkish purple as the ERY concentration increased, making it easy to capture the visualization result. Also, the system showed good sensitivity to ERY ranging from 15 to 135 μM, with a detection limit of 1.78 μM. In addition, the system worked well in the detection of ERY in river water and milk, with the recoveries of 95.57% ∼ 103.20%. These data suggests that this strategy is of considerable potential for practical applications and it provides a new idea for visual detection with portable measurement.

Flexible microfluidic colorimetric detection chip integrated with ABTS·+ and Co@MnO2 nanozyme catalyzed TMB reaction systems for bio-enzyme free detection of sweat uric acid

BackgroundThe development of wearable detection devices that can achieve noninvasive, on-site and real-time monitoring of sweat metabolites is of great demand and practical significance for point-of-care testing and healthcare monitoring. Monitoring uric acid (UA) content in sweat provides a simple and promising way to reduce the risk of gout and hyperuricemia. Traditional bioenzyme based UA assays suffer from high cost, poor stability, inconvenience for storage and easy deactivation of bioenzymes. Wearable microfluidic colorimetric detection device for sweat UA detection has not been reported. The development of novel wearable microfluidic colorimetric detection chip with no requirement of bioenzymes for sweat UA detection is of great importance for health care monitoring. ResultsFirstly, Co@MnO2 nanozyme with high oxidase-like activity was synthesized and characterized. Co@MnO2 can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) directly to generate blue-green colored ox-TMB. Green colored 2,2′-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) radical (ABTS·+) was produced by the oxidation of ABTS by potassium persulfate. UA exhibits distinct quenching effect on Co@MnO2 catalyzed TMB colorimetric reaction system and ABTS·+ based colorimetric system, leading to obvious color fading of the two colorimetric systems. Then, a flexible microfluidic colorimetric detection chip for UA detection was fabricated by assembling Co@MnO2/TMB modified paper chips and ABTS·+ modified paper chips into a polydimethylsiloxane (PDMS) microfluidic chip. The fabricated microfluidic colorimetric detection chip exhibits good linear relationship for sweat UA detection. The linear range is from 20 to 200 μmol/L with detection limit as low as 6.6 μmol/L. Good results were obtained for the detection of UA in actual sweat from three volunteers. SignificanceThis work provides two bio-enzyme free colorimetric detection systems for UA detection. Furthermore, a simple, low-cost and selective flexible wearable microfluidic colorimetric detection chip was fabricated for noninvasive and on-site detection of sweat UA, which holds great application potential for personal health monitoring and point-of-care testing.

Nanozyme-induced deep learning-assisted smartphone integrated colorimetric and fluorometric dual-mode for detection of tetracycline analogs

In this work, a colorimetric and fluorescent dual-mode probe controlled by NH2-MIL-88 B (Fe, Ni) nanozymes was developed to visually detect tetracycline antibiotics (TCs) residues quantitatively, as well as accurately distinguish the four most widely used tetracycline analogs (tetracycline (TC), chrycline (CTC), oxytetracycline (OTC), and doxycycline (DC)). Colorless substrate 3,3′,5,5′-tetramethylbenzidine (TMB) may be oxidized to blue oxidized TMB by the Fe Fenton reaction, which was catalyzed by the NH2-MIL-88 B (Fe, Ni) nanozyme with POD-like activity. The colorimetric detection system allows TCs to interact with NH2-MIL-88 B (Fe, Ni). This inhibits the production of ·OH, weakens the oxidation process of TMB, and ultimately lightens the blue color in the system by blocking the electron transfer between NH2-MIL-88 B (Fe, Ni) and H2O2. Furthermore, TCs can interact with NH2-MIL-88 B (Fe, Ni) as a result of the internal filtering effect, which causes the fluorescence intensity to decrease as TCs concentration increases. Additionally, a portable instrument that combines a smartphone sensing platform with colorimetric and fluorescent signals was created for the quick, visual quantitative detection of TCs. The colorimetric and fluorescent dual-mode nano platform enables color change, with detection limits (LODs) of 0.182 μM and 0.0668 μM for the spectrometer and smartphone sensor, respectively, based on the inhibition of fluorescence and enzyme-like activities by TCs. Overall, the colorimetric and fluorescence dual-mode sensor has good stability, high specificity, and an efficient way to eliminate false-positive issues associated with a single detection mode.

A novel ultrasensitive chemiluminescence enzyme immunoassay by employment of a signal enhancement of horseradish peroxidase-luminol-hydrogen peroxide reaction for the quantitation of atezolizumab, a monoclonal antibody used for cancer immunotherapy.

This study describes, for the first time, the development and validation of a novel ultrasensitive chemiluminescence enzyme immunoassay (CLEIA) for the quantification of atezolizumab (ATZ), a monoclonal antibody approved by the FDA for treatment of different types of cancer. The assay involved the non-competitive binding of ATZ to its specific antigen (PD-L1 protein). The immune complex of PD-L1/ATZ formed on the internal surface of the plate wells was quantified by a novel chemiluminescence (CL)-producing horseradish peroxidase (HRP) reaction. The reaction employed a highly efficient CL enhancer for the HRP-luminol-hydrogen peroxide reaction which was 4-(imidazol-1-yl)phenol. The conditions of the CLEIA and its detection system were refined, and the optimum procedures were established. The CLEIA was validated in accordance with the guidelines of immunoassay validation for bioanalysis, and all the validation criteria were acceptable. The assay's limit of detection and limit of quantitation were 12.5 and 37.5 pg mL-1, respectively, with a working dynamic range of 25-800 pg mL-1. The assay enables the accurate and precise quantitation of ATZ in human plasma samples without any interferences from endogenous substances and/or the plasma matrix. The results of the proposed CLEIA were favourably comparable with those of a pre-validated enzyme-linked immunosorbent assay using a colorimetric detection system. The CLEIA is characterized by simple and high throughput features. The CLEIA is superior to the existing analytical methodologies for ATZ. The proposed CLEIA has a great value in the quantitation of ATZ in clinical settings for assessment of its pharmacokinetics, therapeutic drug monitoring, and refining the safety profile.

A dual-mode homogeneous electrochemical-colorimetric biosensing sensor for carcinoembryonic antigen detection based on a microfluidic paper-based analysis device.

Dual-mode-based sensors have drawn a lot of interest due to their high accuracy and sensitivity compared to single-response systems. A simple electrochemical and colorimetric dual-mode sensor based on enzyme-linked immunosorbent assay (ELISA), without complex electrode surface modification, was developed for accurate and sensitive detection of carcinoembryonic antigen (CEA). The target CEA is recognized by an antibody coupled to horseradish peroxidase (HRP), which then oxidizes the substrate 3,3',5,5'-tetramethylbenzidine (TMB) to generate both a colorimetric and an electrochemical signal. A paper-based analysis device (μPAD) with dual-mode homogeneous sensing microfluidic was created; three paper-based detection areas for colorimetric testing, and a two-electrode embedded detection area for electrochemical testing. When applying colorimetric analysis technology, the linear range of CEA detection is 0.6-40 ng mL-1, and the limit of detection (LOD) is 0.2 ng mL-1. The linear range is 0.1-40 ng mL-1 and the LOD is 0.03 ng mL-1 by applying electrochemical analysis. The visibility and intuitiveness of colorimetry provide a reference for higher sensitivity and quick response of the electrochemical method. A smartphone application (APP) was also developed to realize the dual extraction of colorimetric signals. The colorimetric detection system based on ELISA can provide a new path for the development of electrochemical sensing and makes it have inherent self-verification and self-correction functions and is expected to provide more reliable and accurate detection results.

Activatable prodrug for controlled release of an antimicrobial peptide via the proteases overexpressed in Candida albicans and Porphyromonas gingivalis.

Candida albicans and Porphyromonas gingivalis are prevalent in the subgingival area where the frequency of fungal colonization increases with periodontal disease. Candida's transition to a pathogenic state and its interaction with P. gingivalis exacerbate periodontal disease severity. However, current treatments for these infections differ, and combined therapy remains unexplored. This work is based on an antimicrobial peptide that is therapeutic and induces a color change in a nanoparticle reporter. Methods: We built and characterized two enzyme-activatable prodrugs to treat and detect C. albicans and P. gingivalis via the controlled release of the antimicrobial peptide. The zwitterionic prodrug quenches the antimicrobial peptide's activity until activation by a protease inherent to the pathogens (SAP9 for C. albicans and RgpB for P. gingivalis). The toxicity of the intact prodrugs was evaluated against fungal, bacterial, and mammalian cells. Therapeutic efficacy was assessed through microscopy, disk diffusion, and viability assays, comparing the prodrug to the antimicrobial peptide alone. Finally, we developed a colorimetric detection system based on the aggregation of plasmonic nanoparticles. Results: The intact prodrugs showed negligible toxicity to cells absent a protease trigger. The therapeutic impact of the prodrugs was comparable to that of the antimicrobial peptide alone, with a minimum inhibitory concentration of 3.1 - 16 µg/mL. The enzymatic detection system returned a detection limit of 10 nM with gold nanoparticles and 3 nM with silver nanoparticles. Conclusion: This approach offers a convenient and selective protease sensing and protease-induced treatment mechanism based on bioinspired antimicrobial peptides.

Fully Integrated Microfluidic Platform for Multiplexed Detection of Hunov by a Dynamic Confined-Space-Implemented One-Pot Rpa-Lamp System.

Human norovirus (HuNoV) is the leading cause of nonbacterial acute gastroenteritis, which is highly infectious, rapidly evolving, and easily transmitted through feces. The accurate and early detection of HuNoV subtypes is essential for effective treatment, early surveillance, risk assessment, and disease prevention. In this study, a portable multiplex HuNoV detection platform that combines integrated microfluidics and cascade isothermal amplification, using a streamlined protocol for clinical fecal-based diagnosis is presented. To overcome the problems of carryover contamination and the incompatibility between recombinase polymerase amplification (RPA) and loop-mediated isothermal amplification (LAMP), a Dynamic confined-space-implemented One-pot RPA-LAMP colorimetric detection system (DORLA) is developed by creating a hydrogen bond network. The DORLA system exhibits excellent sensitivity, with detection limits of 10copiesµL-1 and 1copyµL-1 for HuNoV GI and GII, respectively. In addition, a portable diagnostic platform consisting of a thermostatic control module and an integrated 3D-printed microfluidic chip for specific HuNoV capture, nucleic acid pretreatment, and DORLA detection, which enables simultaneous diagnosis of HuNoV GI and GII is developed. A DORLA-based microfluidic platform exhibits satisfactory performance with high sensitivity and portability, and has high potential for the rapid point-of-care detection of HuNoV in clinical fecal samples, particularly in resource-limited settings.

Molecular Self‐Assembly of Au Nanoparticles on a Porous Cellulose Membrane Template for Highly Sensitive Colorimetric Detection of Glucose

AbstractA sensitive glucose colorimetric detection system (Au@QCM) based on quaternized cellulose membrane (QCM) and enzyme‐mimicking Au nanoparticles (AuNPs) was successfully developed via a simple molecular self‐assembly strategy. The positively charged QCM functioned as a template to guide the negatively charged citric acid‐reduced AuNPs uniformly distributed on the surfaces along the pore walls of its porous structure, and thus gave AuNPs an ordered interconnected three‐dimensional network. This electrostatic interaction could effectively prevent the aggregation of the AuNPs and greatly increase their exposed surface area, thus endow the Au@QCM with highly active catalytic properties towards glucose oxidation with glucose oxidase (GOx). The experimental studies showed that the color change of redox indicator 3,3′,5,5′‐tetramethylbenzidine (TMB) can be clearly observed with naked eyes and the absorbance of the oxidized TMB (at 653 nm) was directly proportional to the concentration of glucose. Au@QCM could achieve a sensitive glucose detection with a limit of detection of 0.55 μM and linear response in the range of 0.01–0.5 mM. Besides, it also had good applicability in real samples detection and excellent selectivity to glucose. This novel detection system significantly improved detection performance compared to previous work based on cellulose‐based strips loaded with GOx and horseradish peroxides.

A microfluidic concentration gradient colorimetric system for rapid detection of nitrite in surface water

A microfluidic concentration gradient colorimetric detection system consisting of a microfluidic concentration gradient colorimetric detection chip, a self-built colorimetric signal acquisition box and a self-written smartphone APP was constructed for the rapid, in-field and visual quantitative detection of nitrite. Specifically, nitrite with initial concentration of C0 can be automatically diluted into 8 concentration gradients characterized by arithmetic series, and the concentrations are 0, 0.20 C0, 0.33 C0, 0.46 C0, 0.59 C0, 0.72 C0, 0.86 C0 and C0. The colorimetric signal acquisition box avoided the interference of light spots on data acquisition. Under the optimal experimental conditions, the quantitative detection of nitrite was achieved by the proposed two-step colorimetric method based on the inhibition of AuNPs signal amplification, and the limit of detection (LOD) was 0.14 mg/L. The microfluidic concentration gradient colorimetric detection system was able to detect nitrite as low as 0.43 mg/L and showed a good specificity. The practical application was investigated by analyzing 10 actual samples of river and lake water, pure water and tap water. The recoveries of the microfluidic concentration gradient colorimetric detection system ranged from 94.92% to 105.60%, which indicates that the method had a good application prospect in the detection of practical samples.

Paper-based microfluidic system and chiroptical functionalized gold nano-oval for colorimetric detection of L-Tryptophan

“The development and deployment of a practical and portable technology for on-site chiral identification of enantiomers hold immense significance in the fields of medical and biological sciences. Among the essential amino acids, Tryptophan (Trp) plays a crucial role in human metabolism and serves as a diagnostic marker for various metabolic disorders. In this study, we introduce an innovative approach that combines an enantio-selective ZIF-8-His MOF-MIPs packed-bed centrifugal microfluidic system with an enantioselective colorimetric sensor probe. This system is further integrated with smartphone-based on-site data recording. The basis of this colorimetric sensor's operation lies in the controlled morphology and surface passivation of gold nano-ovals (Au–NOs) through DL-Alanine. To confirm the successful synthesis of the chiral recognition elements, we employed various characterization techniques, including FE-SEM, TEM, FTIR, CD, UV–Vis, zeta potential, DLS, and XRD. Our focus was on optimizing operational parameters for the effective separation and determination of L-chiral tryptophan on-site. The sensor exhibited two linear ranges for L-Trp detection: 0–5.42 and 5.42–80.47 mM, with a detection limit of 0.5 mM. The integrated system possesses advantages such as ease of availability, preparation, high stability, desirable selectivity even in the presence of similar biomolecules, and rapid detection capabilities. Furthermore, our method demonstrated successful enantioselective sensing of L-Trp in various biological samples, including human blood plasma, urine, milk, and bovine serum albumin (BSA), yielding promising results. The integrated microfluidic platform follows a "sample-in and answer-out" approach, making it highly applicable in healthcare, environmental monitoring, food safety analysis, and point-of-care testing. The chiral recognition pretreatment assay and self-contained, automated colorimetric detection on the microfluidic disc represent a promising avenue for cutting-edge research in these domains”.

Adenosine Triphosphatase-Stabilized ZIF-67 as Peroxidase Mimic for Rapid Detection of Glutathione

Zeolitic imidazole framework-67 (ZIF-67) was demonstrated to exhibit intrinsic peroxidase-like activity by using 3,3′,5,5′-tetramethylbenzidine (TMB) as a chromogenic substrate. However, due to the inherent defects in the chemical stability and thermal stability of ZIFs, the peroxidase-like activity of ZIF-67 was severely affected. Therefore, establishing a simple and effective method to enhance the stability of ZIF-67 is necessary. ATP was found to improve the catalytic activity of ZIF-67. On the one hand, compared with ZIF-67, the catalytic efficiency of ZIF-67/ATP increased by 796 %, 5010 % and 570 % at 25 °C, 30 °C and 40 °C, respectively. In addition, the catalytic activity of ZIF-67/ATP was also greatly enhanced at pH-4. On the other hand, compared with ATP, the catalytic rate of ZIF-67/ATP increased by 364 % after 10 min of incubation. Inspired by the high catalytic activity of ZIF-67/ATP, we used the ZIF-67/ATP peroxidase-like system for colorimetric detection of glutathione with the limit of detection (LOD) of 0.46 μM. Furthermore, the proposed method provides a perspective on stabilizing the structures of ZIFs and developing a simple and efficient detection method.

Dual amplification–based ultrasensitive and highly selective colorimetric detection of miRNA

In this study, we combined a Pradeep Kumar (PK)-probe with a ligation–transcription–ramified RCA (LTR) dual-amplification system for the isothermal colorimetric detection of miRNA 25-3P, where the PK-probe transformed from its pink color to colorless in the presence of the amplification byproduct pyrophosphate (PPi), thereby allowing the simple naked-eye qualitative detection of the miRNA. Through this double-amplification strategy, the limit of detection reached as low as 91.4 aM—quite extraordinary sensitivity for a colorimetric miRNA detection system based on absorbance readings. Our detection system also operated with high specificity, the result of using two different target-selective ligation steps (linear DNA ligation and circular DNA ligation) mediated by SplintR ligase, and so could discriminate single-mismatched from perfectly matched target sequences. We suspect that this ultrasensitive and selective PK-probe/LTR dual-amplification system should be a great colorimetric diagnostic for the detection of any miRNA with high efficiency.