Wireless electrochemiluminescent biosensors: Powering innovation with smartphone technology

Energy supply and sensor response acquisition can be performed wirelessly, enabling biosensors as Internet of Thing (IoT) tools by linking wireless power supply and electrochemical sensors. Here, we used the electromagnetic induction method to clarify the conditions under which electrochemiluminescence is induced by a simple potential modulation circuit without an integrated circuit on the electrode chip that receives the power. Initially, the potential waveform obtained in a circuit with inductance and capacitance components that resonate with the transmission frequency and a diode for rectification was investigated to clarify the conditions inducing an electrochemiluminescence reaction at the printed electrode. A high-sensitivity complementary metal-oxide semiconductor camera built into the smartphone wirelessly detected the luminescence generated on the electrode chip. The images were quantitatively evaluated using open-source image analysis software which determine the sensitivity of detecting hydrogen peroxide. Glucose oxidase (GOD) encapsulated in a matrix of chitosan polymers and photocrosslinkable polymers was immobilized on a mass-producible and inexpensive printed electrode to maintain high activity. The immobilized membrane suppressed luminescence when immobilized on the working electrode; therefore, the enzyme was immobilized on the counter electrode for glucose measurement over a wide concentration. Thus, luminol electrochemiluminescence was induced on the electrode chip by wireless power supply from a smartphone. Human serum and artificial sweat samples were tested and indicated possibility for actual applications. In this way a fully wireless biosensor was developed with potential as an IoT biosensor.

Controlled silver electrodeposition on gold nanoparticle antibody tags for ultrasensitive prostate specific antigen sensing using electrochemical and optical smartphone detection

One of the current challenges in medicine is to achieve a rapid and unequivocal detection and quantification of extremely low levels of disease biomarkers in complex biological samples. Here, we present the development and analytical evaluation of a low-cost smartphone-based system designed for ultrasensitive detection of the prostate-specific antigen (PSA) using two detection alternatives: electrochemical or optical, by coupling the smartphone with a portable potentiostat or magnifying lenses. An antibody tagged with gold nanoparticles (AuNPs), and indium tin oxide coated polyethylene terephthalate platform (ITO-PET) have been used to develop a sandwich-type immunoassay. Then, a controlled silver electrodeposition on the AuNPs surface is carried out, enhancing their size greatly. Due to such strong nanoparticle-size amplification (from nm to μm), the final detection can be dual, by measuring current intensity or the number of silver-enlarged microstructures generated. The proposed strategies exhibited limit detections (LOD) of 102 and 37 fg/mL for electrochemical and optical detection respectively. The developed immunosensor reaches excellent selectivity and performance characteristics to quantify biomarkers at clinically relevant values without any pretreatment. These proposed procedures could be useful to check and verify possible recurrence after clinical treatment of tumors or even report levels of disease serum biomarkers in early stages.

Innovative approaches to suppress non-specific adsorption in molecularly imprinted polymers for sensing applications

Molecularly imprinted polymers (MIPs) are synthetic antibodies developed to bind selectively with specific molecules. They function through a particular recognition process involving their cavities and functional groups. Nevertheless, functional groups located outside these cavities are the main cause of non-specific molecule binding, thus reducing the effectiveness of MIPs in sensing applications. This work focused on enhancing the selectivity and performance of MIPs through electrostatic modification with surfactants. The study investigates the use of two surfactants, namely sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB), to eliminate non-specific adsorption in MIPs. The binding isotherms of the target molecule sulfamethoxazole (SMX) on MIPs and non-imprinted polymers (NIPs) were analyzed, showing higher adsorption capacity of MIPs due to the specific cavities. The modification with SDS or CTAB effectively eliminated non-specific adsorption in MIPs. The kinetic adsorption behavior further demonstrated the efficacy of MIP+--SDS/CTAB in the selective adsorption of SMX. Calibration curves showcase the methodology's analytical capabilities, achieving low limit of detection for SMX 6 ng mL-1 using MIP +-SDS. The stability study confirmed that the developed MIP +/--SDS/CTAB remains stable even at high temperatures, demonstrating its suitability for on-site applications. The methodology was successfully applied to detect SMX in milk and water samples, achieving promising recoveries. Overall, the electrostatic modification of MIPs with surfactants emerges as a valuable strategy for enhancing selectivity and performance in target molecule recognition and detection.

Development of a molecularly imprinted membrane for selective, high-sensitive, and on-site detection of antibiotics in waters and drugs: Application for sulfamethoxazole

Sulfonamides are among the widespread bacterial antibiotics. Despite this, their quick emergence constitutes a serious problem for ecosystems and human health. Therefore, there is an increased interest in developing relevant detection method for antibiotics in different matrices. In this work, a straightforward, green, and cost-effective protocol was proposed for the preparation of a selective molecularly imprinted membrane (MIM) of sulfamethoxazole (SMX), a commonly used antibiotic. Thus, cellulose acetate was used as the functional polymer, while polyethylene glycol served as a pore-former. The developed MIM was successfully characterized through scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The MIM was used as a sensing platform in conjunction with a smartphone for optical readout, enabling on-site, selective, and highly sensitive detection of SMX. In this way, a satisfactory imprinting factor of around 3.6 and a limit of detection of 2 ng mL-1 were reached after applying response surface methodologies, including Box-Behnken and central composite designs. Besides, MIM demonstrated its applicability for the accurate and selective detection of SMX in river waters, wastewater, and drugs. Additionally, the MIM was shown to be a valuable sorbent in a solid-phase extraction protocol, employing a spin column setup that offered rapid and reproducible results. Furthermore, the developed sensing platform exhibited notable regeneration properties over multiple cycles and long shelf-life in different storage conditions. The newly developed methodology is of crucial importance to overcome the limitations of classical imprinting polymers. Furthermore, the smartphone-based platform was used to surpass the typically expensive and complicated methods of detection.

Dual-emissive Eu(III)-functionalized metal-organic frameworks for visual, rapid, and intelligent sensing of albendazole and albendazole sulfoxide in animal-origin food

Albendazole (ABZ), a benzimidazole-based anthelmintic, is widely used to treat helminth infections. The extensive and improper use of ABZ may cause drug residues in animal-origin food and anthelmintics resistance, which potentially threaten human health. Meanwhile, albendazole sulfoxide (ABZSO), a metabolite of ABZ, also exhibits toxic effects. Therefore, the detection of ABZ and ABZSO in animal-derived food is significantly necessary. Herein, a dual-emission europium fluorescent sensor (EuUHC-30) was rationally designed and constructed. EuUHC-30 exhibits high selectivity and sensitivity towards ABZ and ABZSO with a detection limit of 0.10 and 0.13 μM, respectively. Furthermore, EuUHC-30 was successfully applied for quantification of ABZ and ABZSO in milk and pig kidney, which were verified by HPLC analysis. Moreover, a smartphone-assisted EuUHC-30 fluorescent paper sensor was fabricated for the practical determination of ABZ and ABZSO in real food. Overall, this work provides a visual, rapid, and intelligent method for the detection of ABZ and ABZSO in animal-origin food.

Bifunctional near-infrared fluorescent probe for the selective detection of bisulfite and hypochlorous acid in food, water samples and in vivo

We report the development of a bifunctional near-infrared fluorescent probe (QZB) for selective sensing of bisulfite (HSO3-) and hypochlorous acid (HOCl). The synergistic detection of HSO3- and HOCl was achieved via a C=C bond recognition site. In comparison with the red-fluorescence QZB, two different products with non-fluorescence and paleturquoise fluorescence were produced by the recognition of QZB towards HSO3- and HOCl respectively, which can realize effectively the dual-functional detection of HSO3- and HOCl. QZB features prominent preponderances of dual-function response, near-infrared emission, reliability at physiological pH, low cytotoxicity and high sensitivity to HSO3- and HOCl. The detection of HSO3- in actual food samples has been successfully achieved using QZB. Utilization of QZB-based test strip to semi-quantitatively detect HSO3- and HOCl in real-world water samples by the "naked-eye" colorimetry are then demonstrated. Simultaneously, the determination of HSO3- and HOCl in real-world water sample has been achieved by smartphone-based standard curves. Additionally, the applications of QZB for imaging HSO3- and HOCl in vivo are successfully demonstrated. Consequently, the successful development of QZB could be promising as an efficient tool for researching the role of HSO3-/HOCl in the regulation of redox homeostasis regulation in vivo and complex signal transduction and for future food safety evaluation.

Digital colorimetric sensor for assessment of iodate in food-grade salt based on paper-based analytical device

A digital colorimetric sensor was developed for the on-site measurement of iodate in food-grade salt. It involved a paper-based analytical device (PAD) containing an immobilized iodide/starch reagent and a smartphone as the detection system. Iodate ions produce a blue-black coloration on the PAD, the smartphone captures a digital image of the PAD, and an installed mobile app performs an analysis to generate color values related to the intensity of the color in the PAD. Parameters in the image acquisition and PAD preparation were optimized, and a matrix-matched calibration plot was employed for quantification. The plot exhibited a linear response in the concentration range of 10 to 100 mg iodate kg^-1 of salt, and a detection limit of 2.20 mg kg^-1 was determined. The present method was applied to analyze real samples, and the results agreed well with those obtained using the reference method at the 95% confidence level.

Advanced visual sensing techniques for on-site detection of pesticide residue in water environments

Pesticide usage has increased to fulfil agricultural demand. Pesticides such as organophosphorus pesticides (OPPs) are ubiquitous in world food production. Their widespread usage has unavoidable detrimental consequences for humans, wildlife, water, and soil environments. Hence, the development of more convenient and efficient pesticide residue (PR) detection methods is of paramount importance. Visual detecting approaches have acquired a lot of interest among different sensing systems due to inherent advantages in terms of simplicity, speed, sensitivity, and eco-friendliness. Furthermore, various detections have been proven to enable real-life PR surveillance in environment water. Fluorometric (FL), colourimetric (CL), and enzyme-inhibition (EI) techniques have emerged as viable options. These sensing technologies do not need complex operating processes or specialist equipment, and the simple colour change allows for visual monitoring of the sensing result. Visual sensing techniques for on-site detection of PR in water environments are discussed in this paper. This paper further reviews prior research on the integration of CL, FL, and EI-based techniques with nanoparticles (NPs), quantum dots (QDs), and metal-organic frameworks (MOFs). Smartphone detection technologies for PRs are also reviewed. Finally, conventional methods and nanoparticle (NPs) based strategies for the detection of PRs are compared.

Sensitive colorimetric detection of antibiotic resistant Staphylococcus aureus on dairy farms using LAMP with pH-responsive polydiacetylene

Rapidly and accurately detecting antibiotic-resistant pathogens in agriculture and husbandry is important since these represent a major threat to public health. While much attention has been dedicated to detecting now-common resistant bacteria, such as methicillin-resistant Staphylococcus aureus, fewer methods have been developed to assess resistance against macrolides in Staphylococcus aureus (SA). Here, we report a visual on-site detection system for macrolide resistant SA in dairy products. First, metagenomic sequencing in raw milk, cow manure, water and aerosol deposit collected from dairy farms around Tianjin was used to identify the most abundant macrolide resistance gene, which was found to be the macB gene. In parallel, SA housekeeping genes were screened to allow selective identification of SA, which resulted in the selection of the SAOUHSC_01275 gene. Next, LAMP assays targeting the above-mentioned genes were developed and interpreted by agarose gel electrophoresis. For on-site application, different pH-sensitive colorimetric LAMP indicators were compared, which resulted in selection of polydiacetylene (PDA) as the most sensitive candidate. Additionally, a semi-quantitative detection could be realized by analyzing the RGB information via smartphone with a LOD of 1.344 × 10-7 ng/μL of genomic DNA from a milk sample. Finally, the proposed method was successfully carried out at a real farm within 1 h from sample to result by using freeze-dried reagents and portable devices. This is the first instance in which PDA is used to detect LAMP products, and this generic read-out system can be expanded to other antibiotic resistant genes and bacteria.

Colorimetric detection of H2O2 with Fe3O4@Chi nanozyme modified µPADs using artificial intelligence

Peroxidase mimicking Fe₃O₄@Chitosan (Fe₃O₄@Chi) nanozyme was synthesized and used for high-sensitive enzyme-free colorimetric detection of H₂O₂. The nanozyme was characterized in comparison with  Fe₃O₄ nanoparticles (NPs) using X-ray diffraction, Fourier-transform infrared spectroscopy, dynamic light scattering, and thermogravimetric analysis. The catalytic performance of Fe₃O₄@Chi nanozyme was first evaluated by UV-Vis spectroscopy using 3,3',5,5'-tetramethylbenzidine. Unlike Fe₃O₄NPs, Fe₃O₄@Chi nanozyme exhibited an intrinsic peroxidase activity with a detection limit of 69 nM. Next, the nanozyme was applied to a microfluidic paper-based analytical device (µPAD) and colorimetric analysis was performed at varying concentrations of H₂O₂ using a machine learning-based smartphone app called "Hi-perox Sens++ ." The app with machine learning classifiers made the system user-friendly as well as more robust and adaptive against variation in illumination and camera optics. In order to train various machine learning classifiers, the images of the µPADs were taken at 30 s and 10 min by four smartphone brands under seven different illuminations. According to the results, linear discriminant analysis exhibited the highest classification accuracy (98.7%) with phone-independent repeatability at t = 30 s and the accuracy was preserved for 10 min. The proposed system also showed excellent selectivity in the presence of various interfering molecules and good detection performance in tap water.

ATP Sensing Paper with Smartphone Bioluminescence-Based Detection

Adenosine-5'-triphosphate (ATP) is the primary energy carrier in all living organisms, and its detection in living cells represents a well-established approach. ATP-driven bioluminescence (BL) relying on the D-luciferin-luciferase reaction is a bioanalytical tool widely employed for monitoring hygiene and microbial contamination of foods.Here, we report a straightforward method for ATP BL detection using an ATP sensing paper fabricated with an alternative freeze-dry procedure. The assay can be easily implemented in laboratories equipped with (i) freeze-drying, wax printing, and 3D printing technologies and (ii) instrumentation for BL detection such as benchtop luminometers and portable light detectors including a smartphone camera without the need for additional equipment.

Advanced graphene oxide-based paper sensor for colorimetric detection of miRNA

MicroRNAs (miRNAs), found in blood and body fluids, have emerged as potential non-invasive biomarkers for disease and injury. miRNAs are quantitatively evaluated using typical RNA analysis methods such as the quantitative reverse transcription polymerase chain reaction, microarrays, and Northern blot, all of which require complex procedures and expensive reagents. To utilize miRNAs as practical biomarkers, it will be helpful to develop simple and user-friendly sensors. In this study, a paper-based miRNA sensor was developed by combining two methods: (1) target-recycled DNAzyme (Dz) amplification and (2) graphene oxide-assisted Dz blotting on paper. The Dz spots on paper caused a miRNA-dependent color change in presence of colorimetric reagents and facilitated the quantification of absolute amount of the target miRNA, irrespective of the volume, with high reproducibility. This approach is technologically straightforward and enables quantification of as low as 7.75 fmol miRNA using a portable smartphone.

Smartphone-assisted robust enzymes@MOFs-based paper biosensor for point-of-care detection

Portable devices featured with fast analysis and affordable methodologies for clinical diagnostics have stimulated the rapid development of point-of-care (POC) technologies, potentially lowering the mortality rate. Herein, we demonstrated a portable, robust, and user-friendly intelligent metal-organic frameworks (MOFs) paper device, called smartphone-assisted biomimetic MOFs nanoreactor colorimetric paper (SBMCP), for on-demand POC detection of endogenous biomolecules. The concept of this paper platform was analogous to the intracellular cascades signal transduction, wherein the single/multiple enzymes components trapped within a ZIF-8 exoskeleton allowed the sensitive and selective recognition of target analyte via the accessible micropores network of ZIF-8, and then transferred the recognition event to a visual color signal based on the cascade reaction. Meanwhile, the ZIF-8 exoskeleton also endowed the enzymes with significantly elevated stability. As a result, this robust and portable SBMCP sensor enabled the on-site analysis of different important disease-related biomolecules through modulating the enzyme cascades, combining with a custom-designed smartphone application for signal readout. In the SBMCP assay, no sophisticated instruments or professional skill of the user was required, only 5 μL sample volume was needed, and the whole analysis process could be achieved within a portable MOFs paper and pervasive smartphone, endowing this new assay with the merits of low-cost, time-saving and easy-to-use. We demonstrated this SBMCP sensor was capable of real-time colorimetric detection of glucose and uric acid in diabetes and gout events. It is believed that this portable biosensor platform proposed herein potentially represents promising alternatives for POC diagnosis, especially applicable in developing world and resource-limited settings.