Search Results (202)

Microfluidic paper-based analytical devices (µPADs) convert ordinary cellulose into an active analytical platform where capillary gradients shape transport, surface chemistry guides recognition, and embedded electrodes or optical probes translate biochemical events into readable signals. Progress in fabrication—from wax and stencil barriers to laser-defined grooves, inkjet-printed conductive lattices, and 3D-structured multilayers—has expanded reaction capacity while preserving portability. Detection strategies span colorimetric fields that respond within porous fibers, fluorescence and ratiometric architectures tuned for low abundance biomarkers, and electrochemical interfaces resilient to turbidity, salinity, and biological noise. Applications now include diagnosing human body fluids, checking food safety, monitoring the environment, and testing for pesticides and illegal drugs, often in places with limited resources. Researchers are now using learning algorithms to read minute gradients or currents imperceptible to the human eye, effectively enhancing and assisting the measurement process. This perspective article focuses on the newest advancements in the design, fabrication, material selection, testing methods, and applications of µPADs, and it explains how they work, where they can be used, and what their future might hold. Full article

Singlet oxygen is a type of reactive oxygen species that is typically generated via type II photosensitization reactions. Since 1,3-diphenylisobenzofuran (DPBF), a commonly used chromogenic probe, exhibits peak absorbance at 410 nm for singlet oxygen detection, it severely interferes with blue light irradiation and compounds that absorb in this wavelength region. This study investigated developing and validating a fluorescence-based method using DPBF to quantitatively analyze the type II photosensitizing property of riboflavin (RF) and its heterocyclic flavin derivatives. DPBF fluorescence-based analysis provided more sensitive and practical results than traditional colorimetric methods. It effectively overcomes spectral interference from colored photosensitizers, such as RF and its derivatives, under blue light irradiation (λ peak 447 nm). This method permitted more effective measurement of their activity without interference from their intrinsic color and maintained high linearity and low variation across different sample concentrations, even with short irradiation times. The type II photosensitizing potency of the tested compounds under blue light was consistently ranked as follows: RF > flavin mononucleotide > flavin adenine dinucleotide > lumiflavin > lumichrome. The results suggest that the DPBF fluorescence-based assay is a more effective approach than colorimetric analysis, making it a practical and reproducible tool for assessing the type II photosensitizing properties of diverse compounds. This study also provides a refinement of an existing probe-based assay for relative comparisons under visible light conditions. Full article

A new rhodamine-based fluorescent probe (RDC, rhodamine-based derivative) was rationally designed and synthesized for the highly selective, sensitive, and quantitative detection of Cu²⁺. The probe demonstrated outstanding specificity toward Cu²⁺, even in the presence of competing metal ions (e.g., Al³⁺, Fe³⁺, Cr³⁺, Na⁺, and K⁺), exhibiting negligible interference and confirming its robust anti-interference capability. A spectroscopic analysis revealed that Cu²⁺ induced spirocyclic ring cleavage, resulting in a colorless-to-pink colorimetric transition and enhancement of the yellow–green fluorescence at 590 nm. Upon addition of Cu²⁺, the fluorescence spectrum showed a linear response in the concentration range of 0.4–20 μM, with a correlation coefficient (R²) of 0.9907 and the limit of detection (LOD) calculated to be 0.12 μM. Meanwhile, Job’s plot analysis verified that the binding stoichiometry between RDC and Cu²⁺ was 1:1. The probe exhibits rapid response kinetics (<5 min) and non-destructiveness properties, enabling in vivo imaging. Under stress conditions, Cu²⁺ accumulated predominantly in root tips (its primary target tissue), with the following distribution hierarchy: root tips > maturation zone epidermis > xylem vessels > cortical cell walls. In conclusion, RDC is a well-characterized, high-performance tool with high accuracy, excellent selectivity, and superior sensitivity for plant Cu²⁺ studies, and this work opens new technical avenues for rhodamine-based probes in plant physiology, environmental toxicity monitoring, and rational design of phytoremediation strategies. Full article

It is important to develop a tetracycline (TC) detection method with a simple synthesis method, high sensitivity, and fast detection speed. Herein, a novel sensor was designed using europium-doped boron nitride (BN-Eu) for evaluation on tetracycline (TC). BN-Eu was synthesized by a simple one-step hydrothermal method. Based on the dual-emission fluorescence signal characteristics of BN-Eu, the content of tetracycline was detected by ratio fluorescence sensing. When the TC concentration increased, the fluorescence emission of BN at 449 nm remained nearly constant, the characteristic emission peak of Eu³⁺ at 618 nm was enhanced due to the antenna effect(AE). The ratiometric fluorescence detection of TC in the range of 0.010–1.0 μmol L⁻¹ was achieved with a detection limit of 4.0 nmol L⁻¹. In addition, the detection system underwent a color shift from blue to red under an irradiation of 365 nm as the TC concentration increased. Based on this, TC visual detection was achieved. The colorimetric signal versus the concentration of TC in the range from 0 to 50 μmol L⁻¹ had a good linear relationship with a detection limit of 1.4 μmol L⁻¹. The probe showed good detection performance through the determination of tetracycline content in tetracycline ointment. The prepared BN-Eu probe has fast response, good sensitivity to TC, and has good potential in detecting tetracycline content in complex samples. Full article

The sensitive and efficient detection of ochratoxin A (OTA) is critical for protecting agricultural ecosystems and public health. A dual-mode plasmonic colorimetric/photothermal aptasensor, based on a Mn²⁺-powered DNA walker for mediating gold nanobipyramid (AuNB) growth, is proposed for OTA detection in this study. In sensing the target OTA, the walking DNA (W-DNA) on the magnetic walker probe was independent and then the environment-friendly Mn²⁺ powered the generation of DNAzyme, where abundant thiol-modified DNA (DNA-SH) was produced by autonomous walking. The positively related DNA-SH level could mediate AuNB growth and reflect dual-mode plasmonic signals. Ultrasensitivity is demonstrated with a limit of detection (LOD) value of 48.6 pg mL⁻¹ for colorimetric mode and 37.6 pg mL⁻¹ for photothermal mode. The aptasensor exhibited high specificity (with cross-reactivity values below 6.2% for other analytes) and high reliability for OTA detection. The requisite practicability and accessibility are verified via its application in agricultural byproduct samples. The findings of this study offer an alternative and efficient biosensing pathway for improving detection performance, enabling green, enzyme-free, homogeneous, and dual-mode strategies for monitoring other pollutants. Full article

Phenol red is a widely used, low-cost, label-free colorimetric pH indicator that bridges traditional colorimetric assays with modern quantitative imaging and cell-based screening platforms. Its protonation-dependent absorbance shift (430–560 nm) allows for the real-time monitoring of extracellular acidification, which indirectly reflects cellular metabolism, growth, and respiration. Although phenol red lacks the molecular specificity of genetically encoded or fluorogenic biosensors, it remains useful in systems where pH changes are effective proxies for physiological processes. Existing tissue digestion protocols often overlook key parameters, especially pH control and enzyme cofactor use. This study presents a straightforward, spectrophotometric method to monitor and adjust the pH of low-volume (1 mL) buffered enzymatic dissociation media using phenol red and a plate reader. We titrated dissociation solutions to physiological pH (~7.4) using spectrophotometric pH measurements validated against conventional glass pH probe readings, confirming method reliability. Accurate pH assessment is critical for isolating viable primary cells for downstream applications such as tissue engineering, single-cell omics, and neurophysiological assays. We highlight that papain-based dissociation media supplemented with L-cysteine can be acidic (pH 6.6) if unadjusted, compromising cell viability. This accessible approach enhances reproducibility by promoting pH documentation concerning dissociation conditions that contribute to advancing consistency in biomedical, cellular, neuronal, and tissue engineering research. Full article

A novel, cost-effective, label-free biosensing strategy has been established for real-time quantification of alkaline phosphatase (ALP) activity, integrating the Tyndall effect with smartphone imaging technology. This method utilizes a handheld laser diode to probe the enzyme-triggered in situ assembly of Cu-guanosine monophosphate (Cu-GMP) coordination polymers, which exhibit tunable Tyndall scattering properties. In the absence of ALP, Cu²⁺ ions chelate with GMP to form Cu-GMP coordination polymers, generating an intense Tyndall effect. Conversely, ALP-mediated hydrolysis of GMP disrupts the formation of Cu-GMP coordination polymers, resulting in diminished light scattering. The intensity of the Tyndall effect is directly proportional to the concentration of Cu-GMP coordination polymers, which in turn correlates with ALP activity levels. A comprehensive investigation of experimental parameters was conducted, including pH, incubation temperature, GMP concentration, incubation time, synthesis duration, and CuSO₄ concentration. Under optimized conditions, the developed smartphone-assisted colorimetric assay enables the detection of ALP activity within the range of 0.375–3.75 U/mL, with a limit of detection of 0.184 U/mL. The application of this method to serum samples yielded recovery rates ranging from 102.6% to 109.0%. In summary, this smartphone-based colorimetric platform offers a portable and versatile approach for instrument-free detection of ALP activity, with potential applications in point-of-care diagnostics and resource-limited settings. Full article

Copper is an important environmental pollutant that poses a significant threat to human health and environmental safety. Therefore, the development of methods for detecting Cu²⁺ is of great significance. A novel fluorometric/colorimetric dual-mode sensor for detecting Cu²⁺ was synthesized by Schiff base reaction using fluorescein hydrazide and 8-hydroxyjulonidine-9-carboxaldehyde as raw materials. Cu²⁺ could form a complex with the probe in a stoichiometric ratio of 1:1. Within 1 min, the fluorescence of the probe rapidly quenched at 540 nm, and the absorbance reached a stable state at 452 nm. The color of the solution changed from light yellow to yellow, achieving real-time and visual detection of Cu²⁺. This probe exhibited exceptional selectivity for Cu²⁺. Within the range of 0–12 μM, the fluorescence intensity of the probe demonstrated a strong linear correlation with the concentration of Cu²⁺ (R² = 0.994), with a detection limit of 0.22 µM. In the ultraviolet colorimetric method, when the Cu²⁺ concentration reached 14 μM, the absorbance stabilized (R² = 0.996), and the detection limit for Cu²⁺ was determined to be 0.38 µM. Furthermore, this probe enabled reversible detection of Cu²⁺, and its performance in real water sample analysis and cellular bioimaging was proven to be highly satisfactory. Full article

We have developed a highly sensitive colorimetric probe based on starch–iodine (I₂) crystallization for the precise discrimination of ethanol–water clusters (E-Wc) within binary ethanol–water solutions (E-Ws). This probe enables the identification of specific E-Wc species and their corresponding transition points. Notably, two distinct transition points were identified at ethanol volume fractions of 40–45% and 75–77%. The former corresponds to the structural transition from (H₂O)_m(EtOH) to (H₂O)_m(EtOH)_n, characterized by a significant loss of blue coloration, while the latter signifies the transition from (H₂O)_m(EtOH)_n to (H₂O)(EtOH)_n, as evidenced by alterations in the absorption intensity of the starch–I₂ complex. Mechanistic studies demonstrate that the observed starch–I₂ crystallization is governed by supramolecular E-Wc rather than individual ethanol or water molecules in the binary solution. By leveraging starch–I₂ crystallization as a colorimetric bridge, we establish a direct correlation between E-Wc transitions and the iodine chromogenic effect. This approach enables the visual detection of transitions in colorless supramolecular assemblies, offering new insights into supramolecular science. Furthermore, as a simple, rapid, and visually interpretable detection method, this colorimetric probe holds promising applications in fields such as the food industry and supramolecular science. Full article

Background/Objectives: The accumulation of Nε-carboxymethyllysine (CML), a major advanced glycation end product (AGE), has been implicated in neuronal dysfunction by promoting oxidative stress, endoplasmic reticulum (ER) stress, and dysregulation of amyloid-β (Aβ) metabolism. This study evaluated the neuroprotective properties of coixol, a naturally occurring polyphenolic compound derived from the outer layers of Coix lacryma-jobi L. var. ma-yuen, in a CML-induced injury model using IMR-32 human neuronal-like cells. Methods: Cells were pretreated with coixol (1 μmol/L), N-acetyl-L-cysteine (NALC, 1 mmol/L), or 4-phenylbutyric acid (4-PBA, 200 μmol/L) for 1 h prior to CML (100 μmol/L) exposure for 24 h. Cell viability was determined by colorimetric analysis of 3-(4,5-dimethyl-2-yl)-2,5-diphenyltetrazolium bromide, while intracellular reactive oxygen species (ROS) generation was quantified using a fluorescence-based oxidative stress probe. Activities of key antioxidant enzymes and caspase-3 were determined using commercial assay kits. The expression of Aβ isoforms, amyloidogenic enzymes, ER stress markers, and apoptosis-related signaling proteins was quantified through validated immunoassays. Results: Coixol pretreatment significantly enhanced cell viability by attenuating ROS accumulation and restoring antioxidant enzyme activities. Concurrently, coixol suppressed ER stress signaling via downregulation of the protein kinase R-like ER kinase/C/EBP homologous protein axis and modulated apoptosis by increasing B-cell lymphoma (Bcl)-2, reducing Bcl-2-associated X protein expression, and inhibiting caspase-3 activation and DNA fragmentation. Furthermore, coixol regulated Aβ metabolism by inhibiting the expression of β-site amyloid precursor protein-cleaving enzyme 1 and presenilin 1, while restoring insulin-degrading enzyme and neprilysin levels, leading to reduced accumulation of Aβ40 and Aβ42. Conclusions: Compared to NALC and 4-PBA, coixol demonstrated comparable or superior modulation across multiple pathological pathways. These findings highlight coixol’s potential as a neuroprotective candidate in AGE-associated neurodegenerative conditions. Full article

This study introduces a novel nucleic acid testing (NAT) protocol that integrates rapid deoxyribonucleic acid (DNA) extraction, isothermal amplification, and visual detection to enable efficient analysis of opportunistic pathogens. Polyethylenimine-functionalized iron oxide (PEI-Fe₃O₄) nanoparticles were prepared by combining PEI, acting as a stabilizing agent, with iron salt, which was utilized as the metal ion precursor by the ultrasonication-assisted co-precipitation method, and characterized for structural, optical, and magnetic properties. PEI-Fe₃O₄ exhibited cationic and anionic behavior in response to pH variations, enhancing adaptability for DNA binding and release. PEI-Fe₃O₄ enabled efficient extraction of E. faecium DNA within 10 min at 40 °C, yielding 17.4 ng/µL and achieving an extraction efficiency of ~59% compared to a commercial kit (29.5 ng/µL). The extracted DNA was efficiently amplified by loop-mediated isothermal amplification (LAMP) at 65 °C for 45 min. Pyrogallol-rich poly(tannic acid)-stabilized gold nanoparticles (PTA-AuNPs) served as colorimetric probes for direct visual detection of the DNA amplified using LAMP. The magnetic-nanogold (PEI-Fe₃O₄/PTA-AuNPs) hybrid system achieved a limit of quantification of 1 fg/µL. To facilitate field deployment, smartphone-based RGB analysis enabled quantitative and equipment-free readouts. Overall, the PEI-Fe₃O₄/PTA-AuNPs hybrid system used in NAT offers a rapid, cost-effective, and portable solution for DNA detection, making the system suitable for microbial monitoring. Full article

Nitrosamines, including N-nitroso diethylamine (NDEA) have emerged as pharmaceutical impurities and carcinogenic environmental contaminants of grave public health safety concerns. This study reports on the preparation and first use of cysteine–gold nanoparticles (CysAuNPs) for colorimetric detection of NDEA in human serum albumin (HSA) under physiological conditions. Molecular docking (MD) and molecular dynamic simulation (MDS) were performed to probe the interaction between NDEA and serum albumin. UV–visible absorption and fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM) imaging were used to characterize the synthesized CysAuNPs. These CysAuNPs show a UV–visible absorbance wavelength maxima (λ_max) at 377 nm and emission λ_max at 623 nm. Results from DLS measurement revealed the CysAuNPs’ uniform size distribution and high polydispersity index of 0.8. Microscopic imaging using TEM showed that CysAuNPs have spherical to nanoplate-like morphology. The addition of NDEA to HSA in the presence of CysAuNPs resulted in a remarkable increase in the absorbance of human serum albumin. The interaction of NDEA–CysAuNPs–HSA is plausibly facilitated by hydrogen bonding, sulfur linkages, or by Cys–NDEA-induced electrostatic and van der Waal interactions. These are due to the disruption of the disulfide bond linkage in Cys–Cys upon the addition of NDEA, causing the unfolding of the serum albumin and the dispersion of CysAuNPs. The combined use of molecular dynamic simulation and colorimetric experiment provided complementary data that allows robust analysis of NDEA in serum samples. In addition, the low cost of the UV–visible spectrophotometer and the easy preparation and optical sensitivity of CysAuNPs sensors are desirable, allowing the low detection limit of the CysAuNPs sensors, which are capable of detecting as little as 0.35 µM NDEA in serum albumin samples, making the protocol an attractive sensor for rapid detection of nitrosamines in biological samples. Full article

The N-glycolylneuraminic acid (Neu5Gc), a major salivary acid molecule found on the cell surface of animals such as pigs, cows, and sheep, can be metabolically incorporated into the body through consumption of animal-derived foods like red meat. This leads to an immune response and chronic inflammation in individuals who do not naturally produce Neu5Gc, including humans and poultry, further increasing the risk of cancer. The trans-cleavage activity of Cas12a is activated by the recognition of the target aptamer by the crRNA, resulting in the cleavage of the dual-labeled probe. By combining this with immunochromatographic techniques, we established a chromatographic test strip assay that allows immediate on-site detection of Neu5Gc contamination in non-red meat samples devoid of Neu5Gc. Further optimization enabled specific detection within 25 min with a minimum detectable limit of 10 ng/mL. These analyses successfully detected the spiked samples and actual samples containing Neu5Gc. The developed lateral flow test strips based on aptamer-Cas12a can be utilized for detecting Neu5Gc contamination in non-red meat food products, animal bioproducts, and poultry feeds. Full article

The detection of aliphatic and aromatic biogenic amines (BAs) is important in food spoilage, environmental monitoring, and disease diagnosis and treatment. Existing fluorescent probes predominantly detect aliphatic BAs with single signal variation and low sensitivity, impairing the adaptability of discriminative sensing platforms. Herein, we present a visual chemosensor (galactose-functionalized pyrrolopyrrole aza-BODIPY, PPAB-Gal) that simultaneously detects eight aliphatic and aromatic BAs in a real-time and intuitive way based on their unique electronic and structural features. Our findings reveal that the dual colorimetric and ratiometric emission changes are rapidly produced in presence of eight BAs through a noncovalent interaction (π–π stacking and hydrogen bond)-assisted chromophore reaction. Specifically, other lone-pair electrons containing compounds, such as secondary amines, tertiary amines, NH₃, and thiol, fail to exhibit these changes. As a result, superior sensing performances with distinctly dual signals (Δλ_ab = 130 nm, Δλ_em = 150 nm), a low LOD (~25 nM), and fast response time (<2 min) were obtained. Based on these advantages, a qualitative and smartphone-assisted sensing platform with a PPAB-Gal-loaded TLC plate is developed for visual detection of putrescine and cadaverine vapor. More importantly, we construct a connection between a standard quantitative index for the TVBN value and fluorescence signals to quantitatively determine the freshness of tuna and shrimp, and the method is facile and convenient for real-time and on-site detection in practical application. Furthermore, since the overexpressed spermine is an important biomarker of cancer diagnosis and treatment, PPAB-Gal NPs can be used to ratiometrically image spermine in living cells. This work provides a promising sensing method for BAs with a novel fluorescent material in food safety fields and biomedical assays. Full article

Hypochlorous acid (HClO) serves as a biological mediator and is widely utilized as a disinfectant in food processing and water treatment. However, excessive HClO residues in food and environmental water raise concerns due to the potential formation of carcinogenic chlorinated byproducts and disinfection byproducts (DBPs). Despite its importance, traditional methods for HClO detection often involve complex sample preparation, sophisticated instrumentation, and skilled operators. Herein, we report an aggregation-induced emission (AIE) small molecule fluorescent probe (NYV) that integrates colorimetric and ratiometric fluorescence responses for the detection of HClO. This probe exhibits high sensitivity, with a detection limit of 0.35 $\mathsf{\mu }$M, a rapid response time of 1 min, and a wide linear range (0–142.5 $\mathsf{\mu }$M), along with anti-interference capabilities, making it suitable for real-time monitoring. Furthermore, we have developed a portable solid-state sensor based on probe NYV for the rapid visual detection of HClO. The potential applications of this probe in real sample analysis and bioimaging experiments are demonstrated. Our findings contribute to the development of innovative fluorescent probes for HClO detection, with broad applications in food safety, environmental monitoring, and biomedical research on oxidative stress and ferroptosis. Full article