Point-of-Care Assay of Alkaline Phosphatase Enzymatic Activity Using a Thermometer or Temperature Discoloration Sticker as Readout

A Fenton-like reaction system with analyte-activated catfish effect as an enhanced colorimetric and photothermal dopamine bioassay

Fenton-like reaction systems have been proven to be efficient as powerful promoters in advanced oxidation processes (AOPs) due to their generated reactive oxygen species (ROS), such as ˙OH and ˙O₂^-, which can further oxidize a specific chromogenic substrate like 3,3',5,5'-tetramethylbenzidine (TMB) to generate sensitive color readout and thereby demonstrate more potential in the colorimetric analysis field. However, the inherent drawback of the low rate-limiting step of Fe³⁺/Fe²⁺ conversion in the Fenton-like reaction and its resultant inefficiency for H₂O₂ decomposition hinder its practical applications. We herein communicate an analyte-activated catfish effect based catalysis strategy to promote the Fenton-like reaction, in which dopamine, like a catfish, was added to activate the Fenton-like reaction. By definition, the conversion rate of Fe³⁺ to Fe²⁺ in the proposed Fenton-like reaction can be significantly accelerated through a specific DA-mediated electron transfer process which further promotes the reaction activity in the Fenton-like reaction to generate more ˙OH and ˙O₂^- radicals. As a result, the produced ˙OH and ˙O₂^- radicals in such a reaction system can significantly oxidize TMB indicator into its oxidation product (TMBox) and therefore indicate the corresponding target-dependent color and photothermal signal readout, enabling the successful fabrication of a more sensitive and stable colorimetric and photothermometric DA sensor. More significantly, this strategy can greatly advance the practical application of Fenton-like reactions in the fields of colorimetric and photothermometric bioassays.

A novel copper ion sensing fluorescent probe for fast detection of pyrophosphate and alkaline phosphatase

A Cu²⁺ sensing fluorescent probe is synthesized via a Mannich reaction and is applied in the fluorescence detection of pyrophosphate and alkaline phosphatase.

Magnetic mesoporous CoFe2O4 labels reacted with TMB for use in a sandwiched photothermal immunoassay for thyroglobulin

An innovative photothermal immunoassay with a sandwich-type immunoreaction mode was designed for the sensitive screening of thyroglobulin on capture antibody-coated microtiter plates using a handheld digital thermometer as the readout device.

Four-Channel Photothermal Plate Reader for High-Throughput Nanoparticle-Amplified Immunoassay

We enhanced the sample throughput of microplate-based photothermal detection by using a semicylindrical prism to expand a point laser source to a long beam for illuminating multiple wells. Coupled with four epoxy-coated thermocouples in alignment with wells on a 96-well microplate, four parallel immunoassays of C-reaction protein (CRP) with antibody-conjugated gold nanoparticles can be simultaneously performed. The sample throughput is further increased by mounting the Styrofoam-enclosed microplate onto a translational/elevator stage so that immunoassays and thermocouple rinse/drying cycles can be implemented in a programmed fashion. The automated assay with three rinse/drying cycles takes only 34.5 min for four samples or 8.62 min/sample, whereas the manual mode with a single thermocouple and a point light source requires at least 66 min for just one sample. With careful calibration of the energy distribution of the expanded laser beam and controllable immersion of the thermocouples, excellent well-to-well (RSD = 1.3%) and cycle-to-cycle (RSD = 4.0%) reproducibility can be attained. The temperature changes can be correlated with the CRP concentration by the Langmuir isotherm, and the low limit of detection, 0.52 ng/mL or 4.33 pM, is well below the plasma CRP levels of both healthy people (<5 μg/mL) and patients (10-500 μg/mL). The serum CRP concentrations quantified by our plate reader are in excellent agreement with the immunoturbidimetric results, demonstrating that this cost-effective, robust, and high-throughput mode for microplate-based immunoassays is amenable to detecting biomarkers in many clinical samples.

Photothermal and fluorescent dual-mode assay based on the formation of polydopamine nanoparticles for accurate determination of organophosphate pesticides

A photothermal and fluorescent dual-mode assay for sensitive organophosphate pesticides (Ops) determination is reported based on alkaline phosphatase (ALP)-inhibition-induced formation of polydopamine (PDA) nanoparticles. In the presence of ALP, ascorbic acid 2-phosphate (AAP) can be catalyzed to produce ascorbic acid (AA). AA can reduce MnO₂ nanosheets, further inhibiting the oxidation of dopamine (DA). Ops as an inhibitor for ALP activity prevents the formation of AA and the reduction of MnO₂ nanosheets. Eventually, the formation of PDA nanoparticles is promoted. The inhibitory effect of Ops on ALP activity causes obvious changes of photothermal signals and fluorescence signal at 495 nm. The detection limit (LOD) of dimethoate is 0.1 μM. The method displays excellent sensing capability for the dimethoate assay in real water with good recoveries of 99.4-107.6%. Graphical abstract A photothermal and fluorescent dual-mode biosensor for sensitive Ops detection was reported based on alkaline phosphatase (ALP)-inhibition-induced formation of polydopamine (PDA) nanoparticles. The dual-mode method significantly improved the accuracy and reliability of the results.

Advances in Sensing Technologies for Monitoring of Bone Health

: Changing lifestyle and food habits are responsible for health problems, especially those related to bone in an aging population. Poor bone health has now become a serious matter of concern for many of us. In order to avoid serious consequences, the early prediction of symptoms and diagnosis of bone diseases have become the need of the hour. From this inspiration, the evolution of different bone health monitoring techniques and measurement methods practiced by researchers and healthcare companies has been discussed. This paper focuses on various types of bone diseases along with the modeling and remodeling phenomena of bones. The evolution of various diagnosis tests for bone health monitoring has been also discussed. Various types of bone turnover markers, their assessment techniques, and recent developments for the monitoring of biochemical markers to diagnose the bone conditions are highlighted. Then, the paper focuses on the potential assessment of the recent sensing techniques (physical sensors and biosensors) that are currently available for bone health monitoring. Considering the importance of electrochemical biosensors in terms of high sensitivity and reliability, specific attention has been given to the recent development of electrochemical biosensors and significance in real-time monitoring of bone health.

Design and application of proximity hybridization-based multiple stimuli-responsive immunosensing platform for ovarian cancer biomarker detection

The development of convenient and sensitive multi-readout immunoassay is crucial but highly challenged for meeting the demand of exactness and diversity in early clinical diagnosis. Herein, a split-type multiple stimuli-responsive biosensor was outlined combined with the outstanding superiority of luminol probe-based electrochemiluminescence (ECL) strategy, mimicking enzyme-mediated colorimetric system and portable photothermal effect-induced temperature sensing. Especially, versatile MoS₂ nanosheets (MoS₂ NSs) with distinguished property not only acted as dual-promoter to improve the cathodic ECL of luminol because of its good electrocatalytic activity for dissolved O₂ and favorable photothermal effect for elevating electrode temperature, but also used as nanozyme to regulate subsequent split-type visual colorimetric sensing due to its peroxidase-like activity for the generation of oxidized 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) in ABTS-H₂O₂ colorimetric system. More importantly, the green oxidized ABTS (ABTS^•+) also exhibited strong near-infrared (NIR) laser-triggered photothermal performance, which can be innovatively employed as sensitive photothermal agent for converting biological signals into temperature under the irradiation of NIR laser, accomplishing more simpler temperature quantitative detection by a portable thermometer. Furthermore, on account of the affinity discrepancy of MoS₂ NSs to single-stranded and double-stranded nucleic acids, a label-free proximity hybridization-based multifunctional assay platform was proposed for target detection with human epididymis-specific protein 4 (HE4) as model protein, demonstrating good analytical performances. Significantly, this innovative work not only enriches the foundational study of multi-model biosensing based on the unitary material but also provides an unambiguous guideline for exploring more accurate and simpler point-of-care diagnosis.

Enhanced Thermometric Sensor for Arsenate Analysis Based on Dual Temperature Readout Signaling Strategy

New methods for portable detection of arsenate are still in urgent need. Herein, we explored a simple but sensitive thermometric strategy for arsenate determination without complex instruments and skilled technicians. Cobalt oxyhydroxide (CoOOH) nanoflakes, can ingeniously decompose hydrogen peroxide into oxygen in a sealed reaction vessel, accompanied by marked pressure and significant temperature increase due to the exothermic reaction effect (ΔH = -98.2 kJ/mol). The increased pressure then compelled a certain amount of H₂O overflowing from the drainage device into another vessel, leading to a significant temperature decrease due to the preloaded ammonium nitrate (NH₄NO₃) and its good dissolution endothermic effect (ΔH = 25.4 kJ/mol). In the presence of arsenate, the catalytic activity of CoOOH nanoflakes for H₂O₂ decomposition was inhibited dramatically, resulting in an obvious decrease of the pressure, weighting water and temperature response. The two temperature responses with increasing and decreasing feature were easily measured through a common thermometer, and exhibited an effective signaling amplification via coupling both "signal-on" and "signal-off" temperature readout elements. The obtained dual superimposing temperature readout exhibits a good linear with the concentration of arsenate with a lower detection limit (51 nM, 3.8 ppb). Compared to the inductively coupled plasma mass spectrometry, this enhanced thermometric strategy provides a simple, rapid, convenient, low cost, and portable platform for sensing arsenate in real environmental water.

Target-triggered aggregation of gold nanoparticles for photothermal quantitative detection of adenosine using a thermometer as readout

Colorimetric platform using the aggregation of gold nanoparticles (AuNPs) is a pretty simple method for biosensing, but advanced instruments such as specterophotometer is still needed to achieve accurately quantitative readout. Aggregated AuNPs exhibit excellent photothermal properties under near-infrared laser irradiation, which is significantly different from non-aggregated AuNPs. Herein, given the different photothermal effect, we translated the AuNPs-based colorimetric assay into a photothermal assay for the quantitative detection of adenosine using a thermometer as readout. Short single-stranded DNA (ssDNA, adenosine aptamer) was adsorbed on the surface of AuNPs and hence prevented the aggregation of AuNPs under high ionic concentration. The presence of adenosine caused the structural change of ssDNA and the AuNPs became aggregated. The enhanced temperature under NIR-laser irradiation has a linear response to the concentration of adenosine in the range of 2.0-50.0 μM. The detection limit was 1.7 μM. This proposed method is portable, easy and applicable to the quantitative assay of other targets by simply replacing of the sequence of ssDNA.

A simple thermometer-based photothermometric assay for alkaline phosphatase activity based on target-induced nanoprobe generation

Alkaline phosphatase (ALP)-induced in situ generation of Prussian blue nanoparticles for photothermometric ALP detection.

Intelligent Platform for Simultaneous Detection of Multiple Aminoglycosides Based on a Ratiometric Paper-Based Device with Digital Fluorescence Detector Readout

A digital fluorescence detector (DFD), a handheld fluorescence detection device, can convert the fluorescence signal of samples into the corresponding fluorescer concentration. Herein, by adopting a DFD as the readout, a novel intelligent platform was developed based on a ratiometric paper-based device (RPD) for multiple aminoglycoside detection. There are five layers and four parallel channels contained in the designed RPD, functioning as reagent storage, fluidic path control and signal processing, respectively. The rationale of this design lies in the fact that aptamer/graphitic carbon nitride nanosheet (Apt/g-C₃N₄ NS) modified layers can catalyze o-phenylenediamine to fluorescent 2,3-diaminophenazine (DAP) in the presence of H₂O₂. When Apt was removed from nanosheets via the Apt-target reaction, the peroxidase-like activity would be decreased, thus decreasing the production of DAP. All the changes of the fluorescence DAP signal can be read out using a portable DFD. Based on the DFD signal change related to the concentration of the target, a quantitative reaction platform was established. Furthermore, the sample flow and Apt-target reaction time can be reasonably regulated using the H₂O₂-cleavable hydrophobic compound modified layer placed between the target recognition region and detection region. Then, the practicality of this platform was verified through realizing sensitive analysis of streptomycin, tobramycin, and kanamycin simultaneously. Overall, with merits including portability and ease of operation, the platform shows great potential in on-site simultaneous detection of multiple targets, especially in resource-limited settings.