Smartphone Readout Research Articles

On paper synthesis of multifunctional CeO2 nanoparticles@Fe-MOF composite as a multi-enzyme cascade platform for multiplex colorimetric detection of glucose, fructose, sucrose, and maltose

This study reports an economical and portable point-of-care (POC) monitoring device based on artificial multi-enzyme cascade systems for multiple detection purposes. The device was made up of a disposable three dimensional microfluidic paper-based analytical device (3D μPAD) with multiple detection zones and a smartphone readout. On-paper synthesis of a multifunctional mimetic composite, based on the CeO2 nanoparticles embedded in the amino-functionalized Fe metal-organic frameworks (CeO2@NH2-MIL-88B(Fe)), for cascade reactions was the main achievement of this work. The 3D μPAD was applied for simultaneous quantification of glucose, fructose, sucrose and maltose, and the detection process consisted of the enzymatic reaction of each sugar by anchored enzymes on the metal-organic frameworks (MOF) and successive oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). Utilizing the new artificial mimicking system improved the color development uniformity and resulted in a reliable detection tool, with excellent detection limits in the range of 20–280 μM. It was directly applied to analyze the sugars levels of human total blood, urine, semen, honey and juice samples with the relative errors of less than 7.7% compared with the HPLC method. The cost-effective and easy-to-use μPAD has a great potential to be used in either medical diagnostics or the food industry. Also, it can be considered as a competitive POC method for patients in disadvantaged communities or emergencies.

Colorimetric aptasensor for on-site detection of acetamiprid with hybridization chain reaction-assisted amplification and smartphone readout strategy

An instruments-free colorimetric assay is established for acetamiprid detection with hybridization chain reaction (HCR)-based amplification strategy. Hairpin probes help gold nanoparticles (AuNPs) to resist salt-induced aggregation through sticky ends. In the presence of acetamiprid, aptamer hairpin probe HP opens due to the specifical recognition, then triggers an explosive hybridization between hairpin probes HA-1/2 and numerous hairpin probes are consumed. With the depletion of hairpin probes, the protection weakens and AuNPs suffer from salt-induced aggregation, which results in a color change from pinkish purplish to blue-purple. Under optimal conditions, the assay exhibits high sensitivity for acetamiprid analysis with a detection limit at 1.74 μM. Meanwhile, the aptasensor displays excellent selectivity that only acetamiprid can trigger the HCR and achieve enhanced detection. Worthwhile, based on the color variation, a smartphone readout-based strategy is proposed for visual quantification of acetamiprid, and good practical performance is obtained in real agricultural samples. The above visual method is portable and economic that get rid of advanced instruments, and shows a promising application prospect for on-site detection of acetamiprid.

Nanozyme enhanced paper-based biochip with a smartphone readout system for rapid detection of cyanotoxins in water

Cyanobacterial harmful algal blooms in freshwater systems can produce cyanotoxins, such as microcystins (MCs) and nodularins (NODs), presenting serious threats to human health and ecosystems. Required routine monitoring of cyanotoxins in water samples, as posed by U.S. EPA drinking water contaminant candidate list 5 (CCL5), demands for cost-effective, reliable and sensitive MCs/NODs detection methods. We report the development of a colorimetric paper-based immunochip assisted by nanozyme catalysis with a smartphone readout system for rapid detection of cyanotoxins in water. We show that the introduction of biorthogonal click reaction enables in situ facile self-assembly of multi-layers of peroxidase-like nanozyme onto the anti-MCs/NODs monoclonal antibody. We can detect 13 variants of MCs/NODs even in the sub-microgram per liter range with detection limit of below 0.7 μg/L and satisfactory recovery percentages between 88 and 120% in different water matrices. Our technology shows a good correlation with the well-developed ELISA technology, demonstrating its great potential applications in resource-limited or less-developed regions for on-site and large-scale screening of cyanotoxins in water environment.

A plug, print & play inkjet printing and impedance-based biosensing technology operating through a smartphone for clinical diagnostics

Simplicity is one of the key feature for the spread of any successful technological product. Here, a method for rapid and low-cost fabrication of electrochemical biosensors is presented. This “plug, print & play” method involves inkjet-printing even in an office-like environment, without the need of highly specialized expertise or equipment, guaranteeing an ultra-fast idea to (scaled) prototype production time. The printed biosensors can be connected to a smartphone through its audio input for their impedance readout, demonstrating the validity of the system for point-of-care biosensing. Proper electrodes layout guarantees high sensitivity and is validated by finite element simulations. The introduction of a passivation method (wax printing) allowed to complete the devices fabrication process, increasing their sensitivity. Indeed, the wax allowed reducing the interference related to the parasitic currents flowing through the permeable coating of the employed substrates, which was used for the chemical sintering, thus avoiding the common thermal treatment after printing. As a case study, we used the devices to develop an electrochemical aptamer-based sensor for the rapid detection of neutrophil gelatinase-associated lipocalin (NGAL) in urine – a clinically important marker of acute kidney injury. The aptasensor platform is capable of detecting clinically relevant concentrations of NGAL with a simple and rapid smartphone readout. The developed technology may be extended in the future to continuous monitoring, taking advantage of its flexibility to integrate it in tubes, or to other diagnostic applications where cost/efficiency and rapidity of the research, development and implementation of point of care devices is a must.

A smartphone-based visual biosensor for CRISPR-Cas powered SARS-CoV-2 diagnostics

The pandemic of coronavirus disease 2019 (COVID-19) resulted from novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a worldwide concern. It is imperative to develop rapid, sensitive, and specific biosensing methods. Herein, we developed a CRISPR-Cas12a powered visual biosensor with a smartphone readout for ultrasensitive and selective detection of SARS-CoV-2. Simply, the SARS-CoV-2 derived nucleic acids triggered CRISPR-Cas12a based indiscriminate degradation of a single-stranded DNA that was supposed to link two gold nanoparticles, inducing the dis-aggregation of gold nanoparticles and thus generating observable color changes. This change can be readily distinguished by naked eyes as well as a smartphone with a Color Picker App. The proposed biosensor was successfully applied to detect SARS-CoV-2 gene in synthetic vectors, transcribed RNA and SARS-CoV-2 pseudoviruses. It rendered “single copy resolution” as evidenced by the 1 copy/μL limit of detection of pseudoviruses with no cross-reactivity. When the developed biosensor was challenged with SARS-CoV-2 clinical bio-samples, it provided 100% agreement (both positive and negative) with qPCR results. The sample-to-result time was roughly 90 min. Our work provides a novel and robust technology for ultrasensitive detection of SARS-CoV-2 that could be used clinically.

Efficient and robust dual modes of fluorescence sensing and smartphone readout for the detection of pyrethroids using artificial receptors bound inside a covalent organic framework

In the study, we have developed an efficient and robust method using dual modes of fluorescence sensing and smartphone readout for the detection of pyrethroids using artificial receptors inside a covalent organic framework. Carbazole-conjugated frameworks (CCFs) were used to prepare efficient fluorescent probes that combine stability with light-emitting activity. CN linkages between aldehydes and amines formed Schiff bases, allowing the development of layered structures, creating exceptionally stable frameworks. Artificial receptors that can bind compounds inside the CCFs with high affinity, for both the detection and absorption of λ-cyhalothrin (LC), were constructed using room-temperature reverse microemulsion polymerization. Under optimum conditions, the fluorescence sensing correlation with the concentration of LC showed good linearity in the range of 0.8–175 μg L−1 with a detection limit of 0.368 μg L−1. The smartphone-based visible readout exhibited a good effect, with a detection limit of 4.067 μg L−1, and recovery of 88 %–103% in food samples. A parallel analysis in food samples was conducted by high-performance liquid chromatography, the results showed good consistency, indicating the practicability of the developed method. Dual mode analysis can avoid the disadvantages of a single response, providing excellent sensitivity, specificity, and efficiency through a strong binding force between the target and the artificial receptors.

Femtomolar SARS-CoV-2 Antigen Detection Using the Microbubbling Digital Assay with Smartphone Readout Enables Antigen Burden Quantitation and Tracking.

High-sensitivity severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen assays are desirable to mitigate false negative results. Limited data are available to quantify and track SARS-CoV-2 antigen burden in respiratory samples from different populations. We developed the Microbubbling SARS-CoV-2 Antigen Assay (MSAA) with smartphone readout, with a limit of detection of 0.5 pg/mL (10.6 fmol/L) nucleocapsid antigen or 4000 copies/mL inactivated SARS-CoV-2 virus in nasopharyngeal (NP) swabs. We developed a computer vision and machine learning-based automatic microbubble image classifier to accurately identify positives and negatives and quantified and tracked antigen dynamics in intensive care unit coronavirus disease 2019 (COVID-19) inpatients and immunocompromised COVID-19 patients. Compared to qualitative reverse transcription-polymerase chain reaction methods, the MSAA demonstrated a positive percentage agreement of 97% (95% CI 92%-99%) and a negative percentage agreement of 97% (95% CI 94%-100%) in a clinical validation study with 372 residual clinical NP swabs. In immunocompetent individuals, the antigen positivity rate in swabs decreased as days-after-symptom-onset increased, despite persistent nucleic acid positivity. Antigen was detected for longer and variable periods of time in immunocompromised patients with hematologic malignancies. Total microbubble volume, a quantitative marker of antigen burden, correlated inversely with cycle threshold values and days-after-symptom-onset. Viral sequence variations were detected in patients with long duration of high antigen burden. The MSAA enables sensitive and specific detection of acute infections and quantification and tracking of antigen burden and may serve as a screening method in longitudinal studies to identify patients who are likely experiencing active rounds of ongoing replication and warrant close viral sequence monitoring.

On paper synthesis of metal-organic framework as a chemiluminescence enhancer for estimating the total phenolic content of food samples using a smartphone readout

Herein, a novel paper-based chemiluminescence (CL) assay is reported using a smartphone readout for on-site and reliable analytical applications. The CL system was based on the high-performance improving effect of cobalt-imidazole metal-organic framework (CoMOF) on luminol-hydrogen peroxide (H2O2) CL emission. The CoMOF was grown on paper and used as a support for the CL reaction, which led to an intense CL emission and good reproducibility. More importantly, the stability of luminol, as the CL reagent, was greatly improved in the presence of CoMOF. This high stability, along with the high-yield CL emission, makes the device highly suitable for commercialization. Furthermore, using a smartphone as the detector for the developed device made the process easier and more accessible for public usage. In this work, the new paper-based CL smartphone device was used for the detection of the total phenolic content of food samples. Phenolic compounds (PC) are hydroxyl radical scavengers that can effectively quench the CL emission of the luminol–H2O2–CoMOF system. After optimizing the reaction conditions, the system could detect PC at the μg mL−1 level. Detection limits of 0.12, 0.28, 0.46, 0.85, and 1.23 μg mL−1 were obtained for gallic acid, quercetin, catechin, kaempferol, and caffeic acid, respectively. This work is the first report on the practical application of smartphone CL assays for the estimation of PC. The proposed assay is an easy-to-use, low-cost, portable, and suitable assay for on-site screening purposes.

Smartphone-Assisted Robust Sensing Platform for on-Site Quantitation of 2, 4-Dichlorophenoxyacetic Acid Using Red Emissive Carbon Dots

Introduction Pesticide contamination has severely attacked the ecosystem and food safety, gradually becoming an escalating threat to public health [1]. Current laboratory-based pesticides-analyzing conventional apparatus comprising of chromatography [2] and mass spectrometry [3] with satisfactory precision and resolution were limited by on-site monitoring. Hence, the development of convenient sensors for pesticide is of great significance. Herein, we constructed a handheld smartphone-assisted fluorometric platform for on-site quantification of pesticide with excellent selectivity and high selectivity based on the optical features of red-emission carbon dots (CDs) and signal amplification of alkaline phosphatase (ALP). The red emissive CDs whose maximum emission center was located at 605 nm with high stability could shield photodamage and autofluorescence interference and enhance anti-interference capability toward matrix. For accurate quantification, the corresponding images were captured by smartphone, together with 3D-printed auxiliary equipment. Using a self-designed application, color intensity was directly relevant to the concentration of analyte pesticide. It is believed that the proposed smartphone-based handheld platform could afford experience for designing neotype sensing strategy in pesticides monitoring. Method For smartphone-based quantitative analysis 2, 4-D, 50 μL various concentrations of 2, 4-D and 50 μL of ALP (7.0 U L-1) were equilibrated at 37 ºC for 10 min. Following, 120 μL of ascorbic acid-2-phosphate trisodium salt (AAP) (100 μmol L-1) containing Tris-HCl buffer were added for incubating another 10 min at 37 ºC and 160 μL CDs/CoOOH composite solution was added to the mixture. After equilibrated for 10 min, the cuvette was inserted into the 3D-printed smartphone reader to obtain the FL photo under the excitation of 532 nm laser. Then, the displayed photo image was directly analyzed by App installed on smartphone. Results and Conclusions Given the design and exploration above, we can directly detect 2, 4-D concentrations in real-time by collecting the optical image of sample. The collected images brightness of the probe solution was in negative connection with 2, 4-D concentrations. Coupling with the FCSMP software, the smartphone readout gray values of various analyte concentrations were acquired in Figure 1. The linear relationship (R2 = 0.990) between smartphone readout gray value and the concentration of 2, 4-D was I = 46.14825 – 2.26776 [2, 4-D], with a LOD of 100 μg L-1 (3σ). Although weaker than the FL spectrometry method on the basis of identical system, that the integrated smartphone-connected sensor displayed comparable liner range and LOD compared with other reported methods was worth noting. The results of 2, 4-D detection demonstrated that the smartphone-assisted fluorometric sensing platform possessed a low requirement for sample volume (50 μL), rapid (30 min) and easy readouts for POC testing.In summary, we have constructed an innovative and portable smartphone-based POC platform for precise quantification of 2, 4-D in a good sensitivity and excellent selectivity manner based on CDs/CoOOH composite. Employing CDs/CoOOH composite as signal indicator, a simple but potentially promising biosensor with outstanding anti-interference capability and good sensitivity have been established. The anti-interference ability was ascribed to the red emissive CDs that could shield background interference. In virtue of introducing ALP, the biosensor performed specific recognition capacity toward 2, 4-D, endowing it high-performance of selectivity. The proposed approach which integrated commercial smartphone, 3D model smartphone accessory and self-designed App into one platform simplified image processing and minimized detection device, effectively circumventing the drawback of bulk instrument with inaccessibility in carrying and complex computer-assistant data analysis. More significantly, the sample-to-answer analysis time of smartphone-based platform is 30 minutes, which was shorter or comparable than that of the immunoassay, chromatograph and enzyme-based strategies. What’s more, such a smartphone optical-sensing system has been triumphantly applied to biological and environmental samples, indicating its robust performance in biological/chemical analysis. Thus, the proposed smartphone-based handheld device provided a promising platform for on-site monitoring pesticide, possessing potential applications in environmental screening, health monitoring, and disease prevention.

Colorimetric point-of-care paper-based sensors for urinary creatinine with smartphone readout

Creatinine is a clinically significant analyte used to diagnose kidney condition. However, the literature still lacks in creatinine sensors fulfilling point-of-care testing requirements. In this paper, we have developed colorimetric paper-based creatinine sensors adhering to point-of-care testing principles. The signal readout is accomplished with a smartphone modified with 3D-printed elements and processed with a self-written application compromising computer vision algorithm for automatic detection of the colored zone. Two colorimetric methods – routinely used Jaffé method and an alternative one with 3,5-dinitrobenzoic acid were both tested and compared. Hue channel intensity from HSV color space and green channel from RGB color space was used as the analytical signal in Jaffé and 3,5-dinitrobenzoate method, respectively. For both kinds of sensors the linear range of the response covered the range significant for urinary analysis, with precision, expressed as RSD, below 5%. Limit of quantification for Jaffé method was 1.05 mmol·L−1 whereas it was 0.82 mmol·L−1 for 3,5-dinitrobenzoate method. The utility of the developed sensors to selectively quantify creatinine in undiluted urine was proved using artificial urine samples and the obtained recoveries were in the range from 70 to 129 %.

Reversible regulation of enzyme-like activity of molybdenum disulfide quantum dots for colorimetric pharmaceutical analysis

Regulating the catalytic activity of nanozymes is significant for their applications in various fields. Here, we demonstrate a new strategy to achieve reversible regulation of the nanozyme's activity for sensing purpose. This strategy involves the use of zero-dimensional MoS2 quantum dots (MQDs) as the building blocks of nanozymes which display very weak peroxidase (POD)-like activity. Interestingly, such POD-like activity of the MQDs largely enhances in the presence of Fe3+ while diminishes with the addition of captopril thereafter. Further investigations identify the mechanism of Fe3+-mediated aggregation-induced enhancement of the POD-like activity and the inhibitory effect of captopril on the enhancement, which is highly dependent on their concentrations. Based on this finding, a colorimetric method for the detection of captopril is developed. This sensing approach exhibits the merits of simplicity, rapidness, reliability, and low cost, which has been successfully applied in quality control of captopril in pharmaceutical products. Moreover, the present sensing platform allows smartphone read-out, which has promising applications in point-of-care testing devices for clinical diagnosis and drug analysis.

A long-term stable paper-based glucose sensor using a glucose oxidase-loaded, Mn2BPMP-conjugated nanocarrier with a smartphone readout.

A simple paper-based analytical device (PAD) for the one-pot detection of glucose was developed herein using an artificial peroxidase-functionalized and glucose oxidase (GOx)-loaded pluronic-based nanocarrier (PNC). Mn2BPMP (BPMP; 2,6-bis[(bis(2-pyridylmethyl)amino)-methyl]-4-methylphenolate), an artificial peroxidase, was conjugated to PNC, allowing GOx to be loaded with a very high encapsulation efficiency. In solution, Mn2BPMP-PNC showed higher peroxidase-like catalytic efficiency than did Mn2BPMP at physiological pH. In addition, glucose detection via enzyme cascade reaction between GOx and Mn2BPMP in the GOx loaded-Mn2BPMP-PNC was more sensitive than the simple combination of Mn2BPMP and GOx with excellent selectivity. Subsequently, a PAD was fabricated using a laser printer with an assay substance containing GOx loaded-Mn2BPMP-PNC and peroxidase chromogenic substrate. The prepared Mn2BPMP-PNC-based PAD quantitatively measured glucose in human serum ranging from normal levels to those typical for diabetics as well as in buffer by obtaining RGB (red, green, and blue) color values through smartphone readout or the naked eye. Importantly, the present PNC-based PAD maintained the detection efficiency during storage at room temperature for 6 weeks in contrast to the rapid decrease in detection efficiency obtained for PAD containing Mn2BPMP and GOx without PNC.

Sample-to-answer COVID-19 nucleic acid testing using a low-cost centrifugal microfluidic platform with bead-based signal enhancement and smartphone read-out.

With its origin estimated around December 2019 in Wuhan, China, the ongoing SARS-CoV-2 pandemic is a major global health challenge. The demand for scalable, rapid and sensitive viral diagnostics is thus particularly pressing at present to help contain the rapid spread of infection and prevent overwhelming the capacity of health systems. While high-income countries have managed to rapidly expand diagnostic capacities, such is not the case in resource-limited settings of low- to medium-income countries. Aiming at developing cost-effective viral load detection systems for point-of-care COVID-19 diagnostics in resource-limited and resource-rich settings alike, we report the development of an integrated modular centrifugal microfluidic platform to perform loop-mediated isothermal amplification (LAMP) of viral RNA directly from heat-inactivated nasopharyngeal swab samples. The discs were pre-packed with dried n-benzyl-n-methylethanolamine modified agarose beads used to selectively remove primer dimers, inactivate the reaction post-amplification and allowing enhanced fluorescence detection via a smartphone camera. Sample-to-answer analysis within 1 hour from sample collection and a detection limit of approximately 100 RNA copies in 10 μL reaction volume were achieved. The platform was validated with a panel of 162 nasopharyngeal swab samples collected from patients with COVID-19 symptoms, providing a sensitivity of 96.6% (82.2-99.9%, 95% CI) for samples with Ct values below 26 and a specificity of 100% (90-100%, 95% CI), thus being fit-for-purpose to diagnose patients with a high risk of viral transmission. These results show significant promise towards bringing routine point-of-care COVID-19 diagnostics to resource-limited settings.

Paper-based DNA sensor enabling colorimetric assay integrated with smartphone for human papillomavirus detection

A colorimetric paper-based DNA sensor that relies on the inhibition of PNA-induced AuNPs aggregation was combined with a simple smartphone readout for the point-of-care detection of HPV type 16 DNA.

CRISPR-Cas12a-driven MXene-PEDOT:PSS piezoresistive wireless biosensor

Beyond extraordinary in vivo accurate gene editing and regulation capabilities, the CRISPR-Cas-associated biotechnology has created a new era of in vitro nucleic acid sensing due to its inherent high-efficiency enzyme cleavage activity and robustness. However, most of the existing CRISPR-Cas systems are largely involve fluorescent reporters or lateral flow strips biosensor and can't fully explore their potential applications (sensitivity and field-deployable) due to the lack of effective signal transduction and wireless data transmission with smartphone readout. Herein, a CRISPR-Cas12a-mediated instrument-free based on flexible interdigitated electrodes-modified piezoresistive block [abrasive paper-molded microstructure polydimethylsiloxane (PDMS) and MXene (Ti 3 C 2 T x )-PEDOT:PSS film] was designed for point-of-care of human papillomavirus (HPV)-related DNA with integrated-module smartphone visual readout. Biotin/thiol-modification single-stranded DNA (ssDNA), acts as a linker between Au@Pt nanoparticles (Au@PtNPs) and streptavidin-coated magnetic bead (MB), are non-specifically cleaved by Cas12a when the guide RNA binds to the target HPV-DNA. Released and separated Au@PtNPs efficiently catalyzes H 2 O 2 to O 2 , and further compress the Ti 3 C 2 T x -PEDOT:PSS/PDMS in a 3D-printed home-made pressure-tight vessel, thus causing the increasing current of the whole circuit thanks to contacting deformation of Ti 3 C 2 T x -PEDOT:PSS/PDMS module and interdigital electrode. After integrating the Bluetooth device and wireless sensing technology in the circuit, the current signal of the target DNA can be wirelessly collected and recorded in real-time and further transmitted/displayed to the mobile terminal of the smartphone. This all-in-one detection mode not only bridges the technological gap between biological signal conduction, wireless transmission, and smartphone interface but also improves the portability and the sensitivity (more than one order of magnitude lower than that of traditional CRISPR-Cas12a biosensors). We expect that a powerful CRISPR-Cas12a system coupled with piezoresistive sensor with wireless transmission technology will become a great demonstration and widely used in real-time wireless biomedical analysis, portable point-of-care health monitoring, and molecular diagnostics. • Combining CRISPR Cas12a-based gas reaction with wireless sensor to detect nucleic acid. • Using CRISPR-Cas12a-based mode to obtain high signal transduction capabilities. • The spinous microstructure can effectively respond to external stimuli.

Combining aptamers and antibodies: Lateral flow quantification for thrombin and interleukin-6 with smartphone readout

Graphical representation of the developed assay, showing positive and negative assay results. • Dual use of aptamer and antibodies in one lateral flow method. • Quantification of clinically relevant targets in plasma. • Precise and direct determination of QD-tags by smartphone-based images. Modern strategies in precision medicine require diagnostic tools for fast assessment of biomarkers. A popular and well-established assay format for the rapid detection of disease markers directly at the point of care is the lateral flow assay, which enables medical staff to directly use body fluids such as blood or urine for diagnosis, without the need for a professional laboratory environment. Interleukin-6 and thrombin are clinically relevant biomarkers that are associated with infectious diseases, inflammation, and blood coagulation, and can provide valuable information on the status and treatment responses of patients with COVID-19. This work presents a novel method for the quantification of these biomarkers by using fluorescent green and red quantum dots as labels for interleukin-6 antibodies and thrombin binding aptamers, respectively. For readout, a 3D printed smartphone imager with a built in UV-LED light source is used. Through separation of RGB-channels, the acquired images can be processed to achieve a fully functional duplex lateral flow assay for simultaneous quantification of interleukin-6 and thrombin on the same test line (optical multiplexing). Furthermore, the assay performs well in complex samples (10 % serum samples). In conclusion, this novel combination of antibody and aptamer-based detection in a single lateral flow assay reduces turnaround time, and the user-friendly smartphone imager facilitates availability, particularly in low resource settings.

Colorimetric detection of Cr3+ in dietary supplements using a smartphone based on EDTA and tannic acid-modified silver nanoparticles

A simplistic, portable and low-cost method for the rapid detection of Cr3+ was developed based on a smartphone readout and a co-functionalized silver nanoparticles (AgNPs) system for use as an on-site device in resource-poor areas. The presence of Cr3+ induced aggregation of AgNPs through coordinated complex formation between Cr3+ and stabilizing agents on the NPs surface, resulted in a bright yellow of an AgNPs solution turned to wine red along with a SPR band was red-shifted from 429nm to 625nm. A smartphone with an available free application, called "PhotoMetrix" was used to measure the RGB (red, green, blue) values of the color intensities in the AgNPs system and convert into Cr3+ concentration by using univariate calibration curves in less than 60s. This smartphone-based detection system showed a high selectivity of AgNPs with Cr3+ and gave a positive coefficient correlation (R2=0.9878) between the intensity of channel R and the Cr3+ concentration, with a linear range of 2.0-5.0mgL-1, and a detection limit of 1.52mgL-1. Furthermore, the proposed method has been successfully applied for quantification of Cr3+ in dietary supplement samples. The results obtained were in close agreement with those obtained in FAAS (Flame Atomic Absorption Spectrometry). The developed colorimetric system based on a smartphone readout device exhibits feasibility and reliability for on-site Cr3+ detection in the real samples.

Dual-function 2D cobalt metal-organic framework embedded on paper as a point-of-care diagnostic device: Application for the quantification of glucose

Point-of-care (POC) diagnostic devices play significant roles in delivering vital surveillance information and providing proper and timely care to patients. There is a challenge in the development of new diagnostic tools to overcome their current shortcomings in terms of cost issues, accuracy and performance. Herein, a highly efficient paper-based analytical device based on a 2D metal-organic framework (MOF) has been reported for the colorimetric/fluorometric monitoring of glucose. Because of the inherent bifunctional activity of cobalt-terephthalate MOF (CoMOF) nanosheets, great improvements were made to the stability and performance of glucose oxidase (GOX) and to its catalytic effect on the reaction of o-phenylenediamine (OPD) and H2O2. The exceptional behavior of 2D CoMOF, along with a precise smartphone readout, led to the rapid and sensitive colorimetric/fluorometric detection of glucose in biological samples. Paper modified by CoMOF and GOX was stable for a long time, and a yellow-brown color and a high fluorescence emission were observed after the addition of a low volume of sample and OPD solutions. The probe showed a wide linear effectiveness range of 50 μM-15 mM, with colorimetric and fluorometric detection limits of 16.3 and 3.2 μM, respectively. Despite its great simplicity, the developed probe showed high performance and accuracy for the quantification of glucose.

A microfluidic paper-based analytical device (μPAD) with smartphone readout for chlorpyrifos-oxon screening in human serum

Acute intoxication incidents due to neurotoxic organophosphate (OP) insecticides are occasionally reported, related either to suicidal attempts or occupational exposure due to the misuse of protective equipment. Among them, chlorpyrifos is a compound related to great controversy, which is still authorized and easily accessible in many countries around the world. However, to screen for its exposure markers, instrumental methods are commonly applied, which cannot enable rapid monitoring at an early stage of an intoxication. Therefore, in this study, a microfluidic paper-based analytical device (μPAD) able to rapidly screen for chlorpyrifos-oxon, the toxic chlorpyrifos metabolite, in human serum was developed and fully validated. The μPAD combines wax-printed butyrylcholinesterase (BChE) paper sensors, a lab-on-a-chip (LOC) prototype injector and a smartphone as the analytical detector. In principle, the wax-printed strips with adsorbed BChE are embedded into LOC injectors able to deliver samples and reagents on-demand. A smartphone reader was used to monitor the color development on the strips providing binary qualitative results. μPAD method performance characteristics were thoroughly evaluated in terms of specificity, detection capability (CCβ) and ruggedness. The developed analytical platform is rapid (results within 10 min), cost-efficient (0.70 €), potentially applicable at the point-of-need and attained a low CCβ (10 μg L−1 in human serum). Finally, μPAD characteristics were critically compared to well-established methods, namely an in-house BChE microplate assay and liquid chromatography tandem mass spectrometry.

Thread-based multiplexed sensor patch for real-time sweat monitoring

Sensor platforms that exploit the fibrous textile threads as substrates offer great promise since they can be directly sewn, woven or stitched on to any clothing. They can also be placed directly in intimate contact with the skin. In this work, we present a thread-based sensing platform in the form of a multiplexed sensing patch for continuous simultaneous on-skin monitoring of sweat. The patch performs real-time, on-body measurements of important biomarkers present in sweat such as electrolytes (sodium and ammonium ions), metabolites (lactate) and acidity (pH). Flexible threads coated with conductive inks were used as sensing electrodes. Selective potentiometric detection of electrolytes and pH was made possible through ion-selective membrane deposition and pH-sensitive polyaniline coating on threads, respectively. An amperometric enzymatic sensing scheme with lactate oxidase was used for the detection of lactate. An array of the thread sensors is integrated onto a patch with connectivity to a miniaturized circuit module containing a potentiostat, microprocessor and wireless circuitry for wireless smartphone readout. Extensive in vitro validation and an in vivo human pilot study involving a maximal exertion test show the promise of this platform for real-time physiological monitoring of human performance/fitness under stress, as well as diagnostic monitoring through sweat analysis.