Smartphone Readout Research Articles

Microwave-assisted synthesis of molecularly imprinted polymers for smartphone-based luminescent hemoglobin one-pot detection

This work introduces a novel strategy to selectively and sensitively determine Hemoglobin (Hb) using a microwave-synthesized molecularly imprinted polymer (MIP) and chemiluminescence (CL) as the detection method. Studies conducted on both MIP and non-imprinted polymer (NIP) evidenced that the MIP material exhibits a high adsorption capacity (48 µg/mg) and an imprinted factor of about 3, in addition to a selective adsorption property towards Hb in the presence of other proteins, whose structures are very similar to that of Hb. The high selectivity and sensitivity of the proposed biosensor were also assured by the CL detection, whose mechanism is based on Hb's ability to enhance luminol oxidation in an alkaline medium in the presence of hydrogen peroxide, emitting a blue light whose intensity is related to the Hb concentration. The emitted light intensities from the CL reaction, directly proportional to Hb concentration, were captured and analyzed using a smartphone and RGB Color application, avoiding the use of sophisticated equipment and facilitating the measurement process. In order to streamline and speed up the detection process, all the experimental steps including Hb adsorption on MIPHb, supernatant removal, CL reaction, and smartphone readout occur in a single 8-well strip. Therefore, the proposed approach offers one-pot detection for the sensitive (LOD = 0.03 µg.mL−1, equivalent to 1.5 nmol.L−1) and selective determination of Hb in blood samples, for biomedical or forensic applications, through a rapid, low-cost, simple, and affordable approach.

Fabrication of fluorescence probe based on molecularly imprinted polymers on red emissive biomass-derived carbon dots coupled with smartphone readout for tyramine determination in fermented meat products.

A fluorescence probe based on molecularly imprinted polymers on red emissive biomass-derived carbon dots (r-BCDs@MIPs) was developed to detect tyramine in fermented meat products. The red emissive biomass-derived carbon dots (r-BCDs) were synthesized by the one-step solvothermal method using discarded passion fruit shells as raw materials. The fluorescence emission peak of r-BCDs was at 670nm, and the relative quantum yield (QY) was about 2.44%. Molecularly imprinted sensing materials were prepared with r-BCDs as fluorescent centers for the detection of trace tyramine, which showed a good linear response in the concentration range of tyramine from 1 to 40µg L-1. The linear correlation coefficient was 0.9837, and the limit of detection was 0.77µg L-1. The method was successfully applied to the determination of tyramine in fermented meat products, and the recovery was 87.17-106.02%. The reliability of the results was verified through high-performance liquid chromatography (HPLC). Furthermore, we combined the r-BCDs@MIPs with smartphone-assisted signal readout to achieve real-time detection of tyramine in real samples. Considering its simplicity and convenience, the method could be used as a rapid and low-cost promising platform with broad application prospects for on-site detection of trace tyramine with smartphone-assisted signal readout.

Dual colorimetric/electrochemical sensor of carbaryl in fruits on microfluidic paper-based analytical device connected with smartphone readout

A dual colorimetric/electrochemical sensor integrated with a microfluidic paper-based analytical device (μPAD) is created for rapid and sensitive detection of cabaryl in fruit. For colorimetric sensor, quercetin modified silver nanoparticle (QCT-AgNPs) is synthesized via self-reduction, resulting in the color change from green to dark green in the presence of cabaryl, which can be readily observed via naked eyes. This colorimetric sensor provides a linear response of 5 – 50 μM quantified by Image J software. For electrochemistry, AgNPs/MXene nanocomposite electrode offers high electrocatalytic activity towards the detection of carbarly with a linear range of 0 – 60 µM and a detection limit of 0.01 µM. The limit of detection values obtained from this dual sensor are lower than a cut-off of carbaryl residue in food, which is 7 mg.kg−1 (35 µM) verifying the desired sensitivity of this platform. Ultimately, this dual sensor is successfully applied for on-site detection of carbaryl in the orange samples read out on the smartphone with satisfactory results.

Self-assembly of cascade nanoenzyme glucose oxidase encapsulated in copper benzenedicarboxylate for wearable sweat-glucose colorimetric sensors with smartphone readout

BackgroundWith the advent of personalized medical approaches, precise and tailored treatments are expected to become widely accepted for the prevention and treatment of diabetes. Paper-based colorimetric sensors that function in combination with smartphones have been rapidly developed in recent years because it does not require additional equipment and is inexpensive and easy to perform. In this study, we developed a portable, low-cost, and wearable sweat-glucose detection device for in situ detection. ResultsThe sensor adopted an integrated biomimetic nanoenzyme of glucose oxidase (GOx) encapsulated in copper 1, 4-benzenedicarboxylate (CuBDC) (GOx@CuBDC) through a biomimetic mineralization process. CuBDC exhibited a peroxide-like effect, cascade catalytic effect with the encapsulated GOx, and increased the enzyme stability. GOx@CuBDC and 3,3,5,5-tetramethylbenzidine were combined to form a hybrid membrane that achieved single-step paper-based glucose detection. Significance and noveltyThis GOx@CuBDC-based colorimetric glucose sensor was used to quantitatively analyze the sweat-glucose concentration with smartphone readings. The sensor exhibited a good linear relationship over the concentration range of 40–900 μM and a limit of detection of 20.7 μM (S/N = 3). Moreover, the sensor performed well in situ monitoring and in evaluating variations based on the consumption of foods with different glycemic indices. Therefore, the fabricated wearable sweat-glucose sensors exhibited optimal practical application performance.

Smartphone based wearable sweat glucose sensing device correlated with machine learning for real-time diabetes screening

BackgroundDiabetes is a significant health threat, with its prevalence and burden increasing worldwide indicating its challenge for global healthcare management. To decrease the disease severity, the diabetic patients are recommended to regularly check their blood glucose levels. The conventional finger-pricking test possesses some drawbacks, including painfulness and infection risk. Nowadays, smartphone has become a part of our lives offering an important benefit in self-health monitoring. Thus, non-invasive wearable sweat glucose sensor connected with a smartphone readout is of interest for real-time glucose detection. ResultsWearable sweat glucose sensing device is fabricated for self-monitoring of diabetes. This device is designed as a body strap consisting of a sensing strip and a portable potentiostat connected with a smartphone readout via Bluetooth. The sensing strip is modified by carbon nanotubes (CNTs)-cellulose nanofibers (CNFs), followed by electrodeposition of Prussian blue. To preserve the activity of glucose oxidase (GOx) immobilized on the modified sensing strip, chitosan is coated on the top layer of the electrode strip. Herein, machine learning is implemented to correlate between the electrochemical results and the nanomaterial content along with deposition cycle of prussian blue, which provide the highest current response signal. The optimized regression models provide an insight, establishing a robust framework for design of high-performance glucose sensor. SignificanceThis wearable glucose sensing device connected with a smartphone readout offers a user-friendly platform for real-time sweat glucose monitoring. This device provides a linear range of 0.1–1.5 mM with a detection limit of 0.1 mM that is sufficient enough for distinguishing between normal and diabetes patient with a cut-off level of 0.3 mM. This platform might be an alternative tool for improving health management for diabetes patients.

Bifunctional oxidase-peroxidase mimicking Fe–Ce MOF on paper-based analytical devices to intensify luminol chemiluminescence: Application for measuring different sugars with a smartphone readout

This study presents a potent paper-based analytical device (PAD) for quantifying various sugars using an innovative bi-nanozyme made from a 2-dimensional Fe/Ce metal-organic framework (FeCe-BTC). The MOF showed excellent bifunctional peroxidase-oxidase activities, efficiently catalyzing luminol's chemiluminescence (CL) reaction. As a peroxidase-like nanozyme, FeCe-BTC could facilitate the dissociation of hydrogen peroxide (H2O2) into hydroxyl radicals, which then oxidize luminol. Additionally, it was also discovered that when reacting with H2O2, the MOF turns into a mixed-valence MOF, and acts as an oxidase nanozyme. This activity is caused by the generated Ce4+ ions in the structure of MOF that can directly oxidize luminol. The MOF was directly synthesized on the PAD and cascaded with specific natural enzymes to establish simple, rapid, and selective CL sensors for the measurement of different sugars. A cell phone was also used to record light intensities, which were then correlated to the analyte concentration. The designed PAD showed a wide linear range of 0.1–10 mM for glucose, fructose, and sucrose, with detection limits of 0.03, 0.04, and 0.04 mM, respectively. It showed satisfactory results in food and biological samples with recovery values ranging from 95.8 to 102.4 %, which makes it a promising candidate for point-of-care (POC) testing for food control and medicinal purposes.

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.

Wearable, disposable and non-enzymatic fluorescence nanosensor for monitoring sweat glucose through smartphone

The promise of non-invasive health monitoring has fuelled the development of wearable biosensors for in situ detection of biological analytes in sweat. This paper presents a new fluorescent nanosensor probe based on boric acid functionalized and heteroatom doped carbon quantum dots (CQDs) embedded in paper-based analytical devices and integrated with a hydrophilic cotton thread-based microfluidic channel for the development of a flexible, wearable, biocompatible, and biodegradable sweat sensor for real-time measurement of sweat glucose concentration via smartphone readout. The morphological, physiochemical, compositional, crystallinity, and optical properties of nanosensors were extensively investigated. CQD particle sizes were found to be widely dispersed, ranging from 2.6 to 7.1 nm, with an average diameter of 4.38 nm. A dual response via fluorescence and colorimetric change was demonstrated for on-site sweat glucose monitoring using a smartphone camera to capture images in RGB (red, green, and blue) format and analyse them simultaneously by a customized android app, with quantitative results displayed on the smartphone. The limit of detection value for in situ measurement of sweat glucose concentration was 1.40 to 2.00 μM (25.25 to 36.13 μg/dL) and the limit of quantification value was 4.67 to 6.69 μM (84.16–120.44 μg/dL) in the pH range of 4.5 to 7.5. The developed sensor's performance metrics were validated using a standard clinical technique, which indicates strong correlation between two methods with Pearson correlation coefficient values of 0.83 and 0.80 for non-diabetic and type- II diabetes patients, respectively. Besides, interference, spike, and recovery studies were carried out with recovery rates ranging from 96.5 to 105.8 %, demonstrating good repeatability and reproducibility. Furthermore, feasible fluorescence quenching processes have been explored. In addition, the disposable and biodegradable nature of the nanosensor probe was studied by throwing it into the soil in the natural environment, where it dissolves almost spontaneously after three weeks.

Integrating PEGylated peptide-oriented bacteria-imprinted matrix and PdPt bimetallic-doped imidazolium zeolite framework-8 for sensitive detection of Escherichia coli with smartphone readout system

Escherichia coli (E. coli) is one of the major foodborne pathogens, and its efficient isolation and detection from complex samples are crucial. Herein, we fabricated a novel hydrophilic-PEGylated peptide-oriented bacteria-imprinted PDMS matrix (HPBIM) for highly efficient capture of E. coli from complex samples. The antibody-free HPBIM possessed a hierarchical structure of imprinted cavities, which were inlaid with peptide-functionalized SiO2 (SiO2@peptide). Meanwhile, PEGylation was performed on the non-imprinted region of HPBIM to limit the non-specific absorption. So HPBIM could specifically capture target E. coli due to the synergistic effect of peptide affinity, bacteria-imprinting and PEGylation of non-imprinted region. Additionally, a new polyethylene glycol-covered / boronic acid-modified PdPt bimetallic-doped ZIF-8 (PBPPZ) was prepared for electively labeling E. coli captured by HPBIM. PBPPZ exhibited excellent peroxidase-like activity and could generate sensitive output signals, which could be further quantitatively determined by smartphone readout device. To prove the practicability, we proposed an innovative HPBIM-PBPPZ strategy, in which the HPBIM first selectively captured E. coli, then the PBPPZ specific labeled E. coli and oxidized colorless substrate into colored product, and finally the change in color was quantitatively determined by a smartphone readout device equipped with a Color Grab APP. The biomacromolecule-free HPBIM-PBPPZ strategy exhibited excellent sensitivity with limit of detection of 69 CFU mL−1 for grapefruit juice and 257 CFU mL−1 for milk, and was successfully applied in the determination of E. coli in spiked sample with recovery and relative standard deviation in the range of 88.1–106.7% and 4.0–7.8%, respectively. Therefore, we believe that the HPBIM-PBPPZ strategy has great potential to become a powerful tool for the ultrasensitive detection of pathogens in complex biological samples.

An “On‐Site Transformation” Strategy for Electrochemical Formation of TiO2 Nanoparticles/Ti3C2Tx MXene/Reduced Graphene Oxide Heterojunction Electrode Controllably toward Ultrasensitive Detection of Uric Acid

Ascribing to the abundance of Ti element, exceptional electrical conductivity, and electrocatalytic performance, titanium carbide MXene (Ti3C2Tx, MX) is considered as an ideal conductive matrix and employed for in situ preparation of promising TiO2 NPs@MX/reduced graphene oxide (rGO) heterojunction electrodes for uric acid (UA) detection. However, the incapability of achieving the controllable growth and synthesis of TiO2 nanoparticles (NPs) on MX nanosheets is a bottleneck in fabricating optimal and controllable TiO2 NPs@MX hybrid. Herein, an “on‐site transformation strategy” is developed to synthetize TiO2 NPs@MX/rGO heterojunction platform controllably by in situ electrochemical oxidizing MX nanosheets at various treatment times. The proposed approach allows for the greater operability to controllably grow and synthetize TiO2 NPs on the surface of MX nanosheets. The heterojunction electrodes present a linear voltammetric response toward UA in the concentration range of 0.003–0.3 and 0.3–300 μm and a low detection limit of 0.78 nm (S/N = 3). Additionally, a handheld electrochemical system with a smartphone readout is developed for point‐of‐care health monitoring, enabling fast, precise, and specific recognition of UA in real urine samples. The study provides a facile and controllable approach to fabricate TiO2 NPs@MX/rGO heterojunction platform for future use in other biomolecules' detection.

NFC-enabled photothermal-based microfluidic paper analytical device for glucose detection.

This study introduces the development of a photothermal-based microfluidic paper analytical device (PT-µPAD) integrated with near-field communication (NFC) technology and smartphone readout for enzyme-free glucose quantification in human samples. With the properties of gold nanoparticles (AuNPs) both as a nanozyme and as a photothermal substrate, there is no need for costly reagents like enzymes or a readout instrumentation for the selective and sensitive detection of glucose. In PT-µPADs, AuNPs are etched by hydrogen peroxide (H2O2) generated from glucose catalysis. Photothermal detection from the plasmonic heating of these AuNPs when illuminated by a 533nm LED light source is achieved by inserting the PT-µPAD sensor into a portable NFC platform suitable for smartphone readout. Temperature variation is directly proportional to the glucose concentration. After optimization, we acquired a linear range between 5.0 and 20.0 µmol L-1 (R2 = 0.9967) and a limit of detection (LOD) of 25.0 nmol L-1 for glucose. Additionally, while our sensor does not utilize any enzyme, it is remarkably selective to glucose with no effects from interferences. Recovery studies in various human control samples indicated a range of 99.73-102.66% with the highest RSD of 3.53%, making it highly accurate and precise. Moreover, our method is more sensitive than other methods relying on conventional µPADs for glucose sensing. By integrating the potential benefits of microfluidics, nanomaterials as nanozymes, and NFC technology for wireless readout, our sensor demonstrates great promise as an accessible, affordable, and shelf-stable device for glucose quantification. Moreover, this concept can be extended to detect other molecules of interest as a point-of-care (POC) diagnostics device.

A versatile CuCo@PDA nanozyme-based aptamer-mediated lateral flow assay for highly sensitive, on-site and dual-readout detection of Aflatoxin B1

Mycotoxin contaminations in food and environment seriously harms human health. Constructing sensitive and point-of-test early-warning tools for mycotoxin determination is in high demand. In this study, a CuCo@PDA nanozyme-based aptamer-mediated lateral flow assay (Apt-LFA) has been elaborately designed for on-site and sensitive determination of mycotoxin Aflatoxin B1 (AFB1). Benefiting from the rich functional groups and excellent peroxidase-like activity, the CuCo@PDA with original dark color can be conjugated with the specific recognition probe (i.e., aptamer), generating colorimetric signal on the test lines of Apt-LFA via a competitive sensing strategy. The signal can further be amplified in-situ by catalytic chromogenic reaction. Therefore, a visual and dual-readout detection of AFB1 has been realized. The developed Apt-LFA provides a flexible detection mode for qualitative and quantitative analysis of AFB1 by naked-eyes observation or smartphone readout. The smartphone-based LFA platform shows a reliable and ultrasensitive determination of AFB1 with the limit of detection (LOD) of 2.2 pg/mL. The recoveries in the real samples are in the range of 95.11–113.77% with coefficients of variations less than 9.84%. This study provides a new approach to realize point-of-test and sensitive detection of mycotoxins in food and environment using nanozyme-based Apt-LFAs.

A highly sensitive hyperbranched Au plasmonic blackbody immunochromatographic assay for detection of leucomalachite green in fish and shrimp

A novel immunochromatographic assay (ICA) based on hyperbranched Au plasmonic blackbodies (AuPBs) with a smartphone readout was fabricated for the detection of leucomalachite green (LMG) in fish and shrimp products. The ICA was carried out in a competitive immunoassay format with AuPBs as labels. The developed AuPBs-ICA allowed for the LMG detection with a low detection limit (0.15 μg L−1) within 5 min by the smartphone reader. With the label-AuPBs ICA, the color intensity response was linearly related to the concentrations of the LMG (0.2 −1.7 μg L−1). The test line signal could be clearly distinguished at a 1.7 μg L−1 LMG as a cut-off level by the naked eye, which is lower than the conventional colloidal gold nanoparticle (2 μg L−1) and star-shaped nanoparticles (1.9 μg L−1) labeling. LMG contamination in samples was determined with the proposed AuPBs-ICA and the enzyme-linked immunosorbent (ELISA). The AuPBs-ICA results showed good agreement with those from the ELISA. The proposed AuPBs-ICA has the potential to be used as a rapid, sensitive, and simple device for the analysis of LMG residues in fish and shrimp samples.

Droplet-based luminescent sensor supported onto hydrophobic cellulose substrate for assessing fish freshness following smartphone readout.

In this work, two sensitive droplet-based luminescent assays with smartphone readout for the determination of trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) are reported. Both assays exploit the luminescence quenching of copper nanoclusters (CuNCs) produced when exposed to volatile nitrogen bases. In addition, hydrophobic-based cellulose substrates demonstrated their suitability as holders for both in-drop volatile enrichment and subsequent smartphone-based digitization of the enriched colloidal solution of CuNCs. Under optimal conditions, enrichment factors of 181 and 153 were obtained with the reported assays for TMA-N and TVB-N, respectively, leading to methodological LODs of 0.11mg/100g and 0.27mg/100g for TMA-N and TVB-N, respectively. The repeatability, expressed as RSD, was 5.2% and 5.6% for TMA-N and TVB-N, respectively (N=8). The reported luminescent assays were successfully applied to the analysis of fish samples, showing statistically comparable results to those obtained with the reference methods of analysis.

Intrinsic Dual-State Emission Zinc-Based MOF Rodlike Nanostructures with Applications in Smartphone Readout Visual-Based Detection for Tetracycline: MOF-Based Color Tonality.

Dual-state emitters (DSEs) are entities that exhibit fluorescence in both the solution and solid state, which open up a wide range of possibilities for their utilization in various fields. The development of detection platforms using intrinsic luminescent metal-organic frameworks (LMOFs) is highly desirable for a variety of applications. DSE MOFs as a subclass of intrinsic LMOFs are highly attractive due to no need for encapsulation/functionalization by fluorophores and/or using luminescent linkers. Herein, a highly stable intrinsic dual-state blue emission (λem = 425 nm) zinc-based MOF with rodlike nanostructures (denoted as UoZ-2) was synthesized and characterized. To the best of our knowledge, intrinsic DSE of Zn-MOFs with blue emission in the dispersed form in solution and solid-state fluorescence have not been reported yet. When tetracycline (TC) was added, a continuous color evolution from blue to greenish-yellow with dramatic enhancement was observed due to aggregation induced emission (AIE). Thus, a sensitive ratiometry-based visual detection platform, in solution and on paper independently, was designed for detection of TC exploiting the DSE and AIE properties of UoZ-2 alone and UoZ-2:TC. The detection limit was estimated to be 4.5 nM, which is considered to be one of the most sensitive ratiometric fluorescent probes for TC sensing. The ratiometry paper-based UoZ-2 sensor displays a reliable TC quantitative analysis by recognizing RGB values in the on-site TC detection with satisfactory recoveries.

A Smartphone-Based Sensing for Portable and Sensitive Visual Detection of Hg (II) via Nitrogen Doped Carbon Quantum Dots Modified Paper Strip.

The development of portable and cost-effective sensing system for Hg2+ quantitation is highly demanded for environmental monitoring. Herein, an on-site, rapid and portable smartphone readout device based Hg2+ sensing system integrating nitrogen-doped carbon quantum dots (NCDs) modified paper strip was proposed, and the physicochemical properties of NCDs were characterized by high resolution TEM, FTIR, UV-vis absorption spectrum and fluorescence spectral analysis. The modified paper strip was prepared via "ink-jet" printing technology and exhibits sensitive fluorescence response to Hg2+ with fluorescence color of bright blue (at the excitation/emission wavelength of 365/440nm). This portable smartphone-based sensing platform is highly selective and sensitive to Hg2+ with the limit of detection (LOD) of 10.6nM and the concentration range of 0-130nM. In addition, the recoveries of tap water and local lake water were in the range of 89.4% to 109%. The cost-effective sensing system based on smartphone shows a great potential for trace amounts of Hg2+ monitoring in environmental water samples.

An enzyme free self-cascade catalytic system with Au deposited bimetallic organic framework as a dual active nanozyme for glucose detection with a smartphone readout platform

A new kind of dual active biomimetic nanozyme was constructed for the establishment of an enzyme free self-cascade catalytic system. Herein, Au/FeNi-MOF nanozyme was designed and constructed by depositing Au quantum dots on a three-dimensional bimetallic organic framework via electrostatic self-assembly. By regulating the immobilization of Au quantum dots on the surface of FeNi-MOF, Au quantum dots not only exhibited stable glucose oxidase-like activity (GOx-like), but enhanced the peroxidase-like activity (POD-like) of FeNi-MOF. The obtained Au/FeNi-MOF nanozyme with both GOx-like and enhanced POD-like activities was used to mimick the cascade catalytic reaction of natural enzymes, thereby construct an enzyme free self-cascade catalytic colorimetric detection system for glucose. The detection method has a linear range of 0.02–10 mM and a detection limit as low as 15 μM with good accuracy and reproducibility. Based on the above performance, a smartphone readout platform for glucose detection was further developed. In this scheme the smartphone was used to extract and recognize the RGB values of the reaction system which were consequently converted into gray values. We recognized that evaluating glucose levels through a smartphone readout platform has the advantage of simple, convenient, and reliable, while revealing its potential application in medical monitoring.

Fabricating process-electrochemical property correlation of laser-scribed graphene and smartphone-based electrochemical platform for portable and sensitive biosensing

Laser-scribed graphene (LSG), a promising electrode material has attracted special research interest in recent years. Here, the fabricating process-electrochemical property correlation of laser-scribed graphene (LSG) devices was discussed emphatically and a pertinent optimization was performed to achieve better electroanalytical performance. Experiment results indicated that the laser scribing technique possessed great process latitude and reducing laser power and scribing speed facilitated fabricating high-quality graphene electrodes. Benefiting from its binder-free 3D porous network structure and high active/geometric area ratio, the optimized LSG electrode was superior to the screen-printed carbon electrode (SPCE) on electrochemical performance in the [Fe(CN)6]3-/4- redox system. Integrating the LSG electrode with a homemade hand-held detector, a portable electrochemical sensing platform with smartphone readout was developed. It realized a specific detection of H2O2 (linear range: 0.02–3.4 mM, sensitivity: 24.56 μA mM−1 cm−2), glucose (linear range: 0.04–4.0 mM, sensitivity: 16.35 μA mM−1 cm−2) by directly decorating biological enzymes without artificial redox mediator and featured a satisfactory comprehensive performance. The constructed immunosensor for tumor necrosis factor-α exhibited a wide linear range (2–500 pg mL−1) and a 4.3-fold enhancement in sensitivity compared with that of SPCE. With satisfactory selectivity, reproducibility, and sensitivity, the developed smartphone-based electrochemical sensing platform held great promise in accurate detection on the spot. This work also provided a significant reference for tailoring binder-free carbonaceous electrode materials toward the desired application.

A Cas12a-based platform combined with gold nanoparticles for sensitive and visual detection of Alternaria solani

Alternaria solani (A. solani), the causal agent of early blight in potatoes, poses a serious and persistent threat to potato production worldwide. Therefore, developing a method that can accurately detect A. solani in the early stage to avoid further spread is urgent. However, the conventional PCR-based method is not appropriate for application in the fields. Recently, the CRISPR-Cas system has been developed for nucleic acids analysis at point-of-care. Here, we propose a gold nanoparticles-based visual assay combining loop-mediated isothermal amplification with CRISPR-Cas12a to detect A. solani. After optimization, the method could detect 10−3 ng/μL genomic gene of A. solani. The specificity of the method was confirmed by discriminating A. solani from other three highly homologous pathogens. We also developed a portable device that could be used in the fields. By integrating with the smartphone readout, this platform holds significant potential in high-throughput detection of multiple pathogens in the fields.

Blue-green emitting cationic thiazole surfactants-based paper devices for highly sensitive and selective fluorescence detection of chromium oxyanions in wastewater

Two cationic Schiff base sensors; N-(3-(((4E)-2-(2-((2-hydroxynaphthalen-1-yl)methylene) hydrazineyl)thiazol-4(5H)-ylidene)amino)propyl)-N,N-dimethyloctan-1-aminiumbromide (N2Q) and N-(3- (((E)-2-(2-((E)-(2-chloro-7-ethoxyquinolin-3-yl)methylene)hydrazineyl)thiazol-4(5H)-ylidene)amino)propyl)-N,N-dimethyloctan-1-aminium bromide (N3Q) were synthesized and characterized to detect Cr (VI) in the wastewater quite quickly, economically, and accurately. The sensors showed a superior selectivity to Cr (Ⅵ) oxyanions among other anions and cations and the quenching efficiency reached 98% at 125 µM. The fluorescence of the sensors is quenched by Cr (VI) oxyanions via electron transfer, electrostatic, and hydrogen bonding mechanisms as confirmed by optical spectra, FT-IR, Zeta potential, and DFT calculations. The N2Q sensor could lower the detection limits to 34 nM for CrO42- and 13 nM for Cr2O72-, with linear detection ranges of 0.0005–1025 nM. At the same time, the N3Q sensor had a good linear range of 5–125 µM and 0.0005–60 µM with detection limits of 18 and 11 nM for CrO42- and Cr2O72-, respectively. Furthermore, Cr (VI) oxyanions are detected in real samples, with recoveries ranging from 85.56 to 101%. More interestingly, portable, low-cost, and convenient-to-use paper devices are successfully used to visually detect Cr (VI) oxyanions at levels as low as 5 nM. The feasibility of using a smartphone readout device to determine Cr (VI) oxyanions has been established.