Smartphone-based biosensors: A critical review and perspectives

Biosensors for psychiatric biomarkers in mental health monitoring

Psychiatric disorders are associated with serve disturbances in cognition, emotional control, and/or behavior regulation, yet few routine clinical tools are available for the real-time evaluation and early-stage diagnosis of mental health. Abnormal levels of relevant biomarkers may imply biological, neurological, and developmental dysfunctions of psychiatric patients. Exploring biosensors that can provide rapid, in-situ, and real-time monitoring of psychiatric biomarkers is therefore vital for prevention, diagnosis, treatment, and prognosis of mental disorders. Recently, psychiatric biosensors with high sensitivity, selectivity, and reproducibility have been widely developed, which are mainly based on electrochemical and optical sensing technologies. This review presented psychiatric disorders with high morbidity, disability, and mortality, followed by describing pathophysiology in a biomarker-implying manner. The latest biosensors developed for the detection of representative psychiatric biomarkers (e.g., cortisol, dopamine, and serotonin) were comprehensively summarized and compared in their sensitivities, sensing technologies, applicable biological platforms, and integrative readouts. These well-developed biosensors are promising for facilitating the clinical utility and commercialization of point-of-care diagnostics. It is anticipated that mental healthcare could be gradually improved in multiple perspectives, ranging from innovations in psychiatric biosensors in terms of biometric elements, transducing principles, and flexible readouts, to the construction of 'Big-Data' networks utilized for sharing intractable psychiatric indicators and cases.

Microfluidic sensors for the detection of emerging contaminants in water: A review

In recent years, numerous emerging contaminants have been identified in surface water, groundwater, and drinking water. Developing novel sensing methods for detecting diverse emerging pollutants in water is urgently needed, as even at low concentrations, these pollutants can pose a serious threat to human health and environmental safety. Traditional testing methods are based on laboratory equipment, which is highly sensitive but complex to operate, costly, and not suitable for on-site monitoring. Microfluidic sensors offer several benefits, including rapid evaluation, minimal sample usage, accurate liquid manipulation, compact size, automation, and in-situ detection capabilities. They provide promising and efficient analytical tools for high-performance sensing platforms in monitoring emerging contaminants in water. In this paper, recent research advances in microfluidic sensors for the detection of emerging contaminants in water are reviewed. Initially, a concise overview is provided about the various substrate materials, corresponding microfabrication techniques, different driving forces, and commonly used detection techniques for microfluidic devices. Subsequently, a comprehensive analysis is conducted on microfluidic detection methods for endocrine-disrupting chemicals, pharmaceuticals and personal care products, microplastics, and perfluorinated compounds. Finally, the prospects and future challenges of microfluidic sensors in this field are discussed.

Smartphone-based device for rapid and single-step detection of piRNA-651 using anti-DNA:RNA hybrid antibody and enzymatic signal amplification

P-element-induced wimpy testis (PIWI)-interacting RNAs (piRNAs/piRs) are a class of small noncoding RNAs that play a crucial role in regulating various biological processes, including carcinogenesis. One specific piRNA, piR-651, has been reported to be overexpressed in both human blood serum and solid cancer tissues, that can be used a viable biomarker in cancer diagnosis. Early diagnosis of cancer can help reduce the burden of the disease and improve survival rates. In the present work, we report for the first time a smartphone-based colorimetric biosensor for highly sensitive and specific detection of piR-651 thanks to an enzymatic signal amplification, which yielded high colorimetric intensities. Indeed, a heteroduplex DNA:RNA was formed in the presence of piR-651 with the capture DNA probe immobilized on the magnetic beads for easy magnetic separation. Then, a HRP tethered to anti-DNA:RNA (S9.6) was used to reveal the DNA-RNA heteroduplex formed by catalyzing the oxidation of TMB substrate into colorimetric TMBox, which absorbs at 630 nm. The absorbance is positively proportional to the piR-651 concentrations. On the other hand, the colorimetric product of the assay can be photographed with a smartphone camera and analyzed using ImageJ software. Using a smartphone and under optimal conditions, the biosensor responded linearly to the logarithm of piRNA-651 from 8 fM to 100 pM with a detection limit of 2.3 fM and discriminates against other piRNAs. It was also successfully applied to the determination of piRNA-651 levels in spiked human serum.

Evaluating smartphone-based optical readouts for immunoassays in human and veterinary healthcare: A comparative study

Recent advances have significantly enhanced the use of smartphone devices for medical diagnostics. This study uses high-resolution cameras in mobile devices to capture and process bioassay images, enabling the quantification of diverse biomarkers across a range of diagnostic tests conducted on 96-well microplates. The study evaluates the effectiveness of this technology through protein quantification techniques and immunoassays that generate colorimetric responses at specific wavelengths. It includes the assessment of bicinchoninic acid and Bradford protein quantification methods, alongside a conventional immunoassay for detecting mare antibodies in colostrum to monitor foal immunodeficiencies. Further application involves the readout of magneto-actuated immunoassays aimed at quantifying bacteria. The results obtained from benchtop spectrophotometry at 595, 562, and 450 nm are compared with those acquired using a smartphone, which identified color intensities in shades of blue, purple, and yellow. This comparison yields promising correlations for the samples tested, suggesting a high degree of accuracy in the smartphone capability to analyze bioassay outcomes. The analysis via smartphone is facilitated by a specific app, which processes the images captured by the phone camera to quantify color intensities corresponding to different biomarker concentrations. Detection limits of 12.3 and 22.8 μg mL-1 for the bicinchoninic acid assay and 36.7 and 45.4 μg mL-1 for the Bradford are obtained for protein quantification using the spectrophotometer and the smartphone app, respectively. For mare's antibodies in colostrum, the values are 1.14 and 1.72 ng mL-1, while the detection of E. coli is performed at 2.0 x 104 and 2.9 × 104 CFU mL-1, respectively. This approach offers further advantages, including wide availability, cost-effectiveness, portability, compared to traditional and expensive benchtop instruments.

Smartphone-Integrated Wireless Portable Potentiostat to Develop 5th-Generation Dengue Pocket Aptasensor toward Portronicx-Approach

Smartphones' widespread availability and worldwide connection are advancing the idea of mobile-based healthcare and promise to transform the business of biosensors. Biosensors based on smartphones have been investigated in several ways, including employing a smartphone in place of a detector or as an instrumental interface. The current work demonstrates the first successful detection of dengue virus using a smartphone-based pocket sensor combined with a wireless potentiostat. The platform developed comprises a smartphone, a wireless portable potentiostat, an Android app, and a three-electrode setup. The combination of portable diagnostic with electronic application is referred to as "Portronicx", and this is the first time that the term "Portronicx" has been used in a dengue sensor, so the current study has the potential to be commercialized in the market with the tag line "Portronicx-commercialization" in the future. Miniaturization improves alternative setup options in terms of instrument size, affordability, mobility, touch-mobile display, and design versatility. The current work proved the excellent combination of a wireless potentiostat with an aptasensor to detect dengue antigen within 20 s with good LOD (0.1 μg/mL) and easy to carry in their pockets. The created platform also performed effectively in human serum. This study replaced all of the instruments with a lightweight touch smartphone, paving the way for the production of fifth-generation electrochemical aptasensors, with potential implications for healthcare applications on the verge of commercialization.

Quantitative, high-sensitivity measurement of liquid analytes using a smartphone compass

Smartphone ubiquity has led to rapid developments in portable diagnostics. While successful, such platforms are predominantly optics-based, using the smartphone camera as the sensing interface. By contrast, magnetics-based modalities exploiting the smartphone compass (magnetometer) remain unexplored, despite inherent advantages in optically opaque, scattering or auto-fluorescing samples. Here we report smartphone analyte sensing utilizing the built-in magnetometer for signal transduction via analyte-responsive magnetic-hydrogel composites. As these hydrogels dilate in response to targeted stimuli, they displace attached magnetic material relative to the phone's magnetometer. Using a bilayer hydrogel geometry to amplify this motion allows for sensitive, optics-free, quantitative liquid-based analyte measurements that require neither any electronics nor power beyond that contained within the smartphone itself. We demonstrate this concept with glucose-specific and pH-responsive hydrogels, including glucose detection down to single-digit micromolar concentrations with potential for extension to nanomolar sensitivities. The platform is adaptable to numerous measurands, opening a path towards portable, inexpensive sensing of multiple analytes or biomarkers of interest.

Smartphone-based device for point-of-care diagnostics of pulmonary inflammation using convolutional neural networks (CNNs)

In pulmonary inflammation diseases, like COVID-19, lung involvement and inflammation determine the treatment regime. Respiratory inflammation is typically arisen due to the cytokine storm and the leakage of the vessels for immune cells recruitment. Currently, such a situation is detected by the clinical judgment of a specialist or precisely by a chest CT scan. However, the lack of accessibility to the CT machines in many poor medical centers as well as its expensive service, demands more accessible methods for fast and cheap detection of lung inflammation. Here, we have introduced a novel method for tracing the inflammation and lung involvement in patients with pulmonary inflammation, such as COVID-19, by a simple electrolyte detection in their sputum samples. The presence of the electrolyte in the sputum sample results in the fern-like structures after air-drying. These fern patterns are different in the CT positive and negative cases that are detected by an AI application on a smartphone and using a low-cost and portable mini-microscope. Evaluating 160 patient-derived sputum sample images, this method demonstrated an interesting accuracy of 95%, as confirmed by CT-scan results. This finding suggests that the method has the potential to serve as a promising and reliable approach for recognizing lung inflammatory diseases, such as COVID-19.

Universal smartphone-assisted label-free CRISPR/Cas12a-DNAzyme chemiluminescence biosensing platform for on-site detection of nucleic acid and non-nucleic acid targets

The clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein (Cas) (CRISPR/Cas) system enables sensitive and specific detection of biomolecules, thanks to its programmability, high fidelity, and powerful signal amplification capabilities. Herein, a universal smartphone-assisted label-free G-quadruplex (G4) DNAzyme-based chemiluminescence CRISPR/Cas12a biosensing platform (G4CLCas) is firstly described that achieves on-site, ultrasensitive visual detection of nucleic acid and non-nucleic acid targets. The G4CLCas-based sensing platform relies on Cas12a trans-cleavage activation that triggers the cleavage of the G4 DNAzyme, resulting in chemiluminescence signals off/on compared to that of the control. Chemiluminescence signals are captured as images that are quantitatively analyzed and visualized using a smartphone-assisted imaging cartridge. Under optimal conditions, G4CLCas achieves a low limit of detection (LOD) of 8.6 aM (∼5.2 copies/μL) for monkeypox virus (MPXV) DNA within the linear concentration range of 10-300 aM and can accurately quantify viral DNA in spiked samples. G4CLCas can also detect non-nucleic acid targets, whereby it achieves a low LOD value of 84.3 nM for adenosine triphosphate (ATP) within the linear concentration range of 2-2000 μM. Here, a label-free, portable, on-site CRISPR/Cas12a chemiluminescence biosensing platform based on the G4 DNAzyme substrates is proposed with potential applications in clinical detection and bioanalytical chemistry research.

Portable optical fiber biosensors integrated with smartphone: technologies, applications, and challenges [Invited]

The increasing demand for individualized health monitoring and diagnostics has prompted considerable research into the integration of portable optical fiber biosensors integrated with smartphones. By capitalizing on the benefits offered by optical fibers, these biosensors enable qualitative and quantitative biosensing across a wide range of applications. The integration of these sensors with smartphones, which possess advanced computational power and versatile sensing capabilities, addresses the increasing need for portable and rapid sensing solutions. This extensive evaluation thoroughly examines the domain of optical fiber biosensors in conjunction with smartphones, including hardware complexities, sensing approaches, and integration methods. Additionally, it explores a wide range of applications, including physiological and chemical biosensing. Furthermore, the review provides an analysis of the challenges that have been identified in this rapidly evolving area of research and concludes with relevant suggestions for the progression of the field.

Bioengineered cellulosic paper micro-device for serum albumin detection in clinical range

Chronic Kidney Disease (CKD) is becoming one of the major causes of morbidity and mortalities in 21st century. We have developed a bioengineered cellulosic paper device for the quantification of albumin (ALB) in physiological samples. The paper surface was activated and antibodies specific to target biomarker was immobilized on engineered paper surface. Every step after modification was characterized by FTIR, XPS, SPM and optical analysis. Further, the device model was designed using CAD file, and a 3-D cascade device was fabricated with in-built constant light source to provide proper and controlled environment for in-situ image analysis. After adding the sample on the bioengineered paper, the antigen-antibody reaction takes place, after that addition of dye results in change of color from yellow to blueish-green within 40 s. An optical method was employed for the analysis of the images by recognizing the specific area and the color intensity. Additionally, the immunosensor specificity was evaluated on number of molecules that are usually found in the serum sample. The linear dynamic range of the developed immunosensor has been reported to be 1-60 mg/mL, covering the normal as well as clinical range of ALB in physiological samples with a detection limit of 0.049(±0.002) mg/mL. With good precision and recovery, the device was able to successfully determine the ALB concentrations in serum sample. The developed device has simple and user-friendly interface and it may also help diagnosing CKD in personalized settings.

Microfluidic-assisted integrated nucleic acid test strips for POCT

Numerous diseases have posed significant threats to public health, notably the global pandemic of COVID-19, resulting in widespread devastation due to its high infectivity and severity. The nucleic acid lateral flow assay (NALFA) addresses challenges of complexity, cost, and time associated with traditional assays, offering a reliable platform for rapid and precise nucleic acid target detection. NALFA is gaining prominence as a point-of-care testing (POCT) technique, thanks to its user-friendly operation and rapid results. Nevertheless, conventional NALFA relies on specialized technicians and involves labor-intensive steps like DNA extraction and PCR processes, impeding its efficiency. To overcome these limitations, integrating NALFA with microfluidic technology, widely employed in rapid field detection, holds promise. This review comprehensively outlines prevailing strategies for integrating NALFA, encompassing both research initiatives and commercial applications. Addressing the bottleneck of nucleic acid amplification as a rate-limiting step, the review delves into progress in amplification-free NALFA and highlights prevalent signal amplification techniques. Ultimately, the review outlines the future prospect of integrated NALFA development, capturing the technology's evolution and providing valuable insights for academic and commercial endeavors.

Smartphone-integrated paper-based biosensor for sensitive fluorometric ethanol quantification

The development of fluorometric paper-based analytical devices (fPADs) integrated with smartphone for fluorometric quantification of ethanol in an instrument-free and portable setup is described. The NAD+-dependent alcohol dehydrogenase immobilized within chitosan modified paper substate was utilized as a bio-recognition element and enzymatically generated NADH was used as a fluorescent probe. 3D-printed imaging setup which houses a paper chip holder and UV-light emitting device (LED) was developed for rapid, accurate capture of the fluorescent images. The biocompatible chitosan layer covering the paper provides a feasible environment for enzyme immobilization and enhances the fluorescence signal. The developed fPADs exhibited high sensitivity for ethanol detection and has a linear range for ethanol detection from 17 µM to 8.75 mM (R2 =0.99). Additionally, the fPADs were applied to quantify ethanol in four different wine samples including red, white, rose, and sparkling wines successfully. Moreover, the fPADs produce reproducible signals without loss of enzyme activity for at least 14 days and ~80% activity remained till 28 days. Thus, the proposed approach can provide a facile, affordable, portable, and instrument-free tool for the onsite quantification of ethanol in real samples and is applicable for food quality controls.

AQAFI: a bioanalytical method for automated KPIs quantification of fluorescent images of human leukocytes and micro-nano particles

Micro-nanoparticle and leukocyte imaging find significant applications in the areas of infectious disease diagnostics, cellular therapeutics, and biomanufacturing. Portable fluorescence microscopes have been developed for these measurements, however, quantitative assessment of the quality of images (micro-nanoparticles, and leukocytes) captured using these devices remains a challenge. Here, we present a novel method for automated quality assessment of fluorescent images (AQAFI) captured using smartphone fluorescence microscopes (SFM). AQAFI utilizes novel feature extraction methods to identify and measure multiple features of interest in leukocyte and micro-nanoparticle images. For validation of AQAFI, fluorescent particles of different diameters (8.3, 2, 1, 0.8 μm) were imaged using custom-designed SFM at a range of excitation voltages (3.8-4.5 V). Particle intensity, particle vicinity intensity, and image background noise were chosen as analytical parameters of interest and measured by the AQAFI algorithm. A control method was developed by manual calculation of these parameters using ImageJ which was subsequently used to validate the performance of the AQAFI method. For micro-nanoparticle images, correlation coefficients with R2 > 0.95 were obtained for each parameter of interest while comparing AQAFI vs. control (ImageJ). Subsequently, key performance indicators (KPIs) i.e., signal difference to noise ratio (SDNR) and contrast to noise ratio (CNR) were defined and calculated for these micro-nano particle images using both AQAFI and control methods. Finally, we tested the performance of the AQAFI method on the fluorescent images of human peripheral blood leukocytes captured using our custom SFM. Correlation coefficients of R2 = 0.99 were obtained for each parameter of interest (leukocyte intensity, vicinity intensity, background noise) calculated using AQAFI and control (ImageJ). A high correlation was also found between the CNR and SDNR values calculated using both methods. The developed AQAFI method thus presents an automated and precise way to quantify and assess the quality of fluorescent images (micro-nano particles and leukocytes) captured using portable SFMs. Similarly, this study finds broader applicability and can also be employed with benchtop microscopes for the quantitative assessment of their imaging performance.

Analysing olive ripening with digital image RGB histograms

Digital images are commonly used to monitor processes that are based on colour changes due to their simplicity and easy capture. Colour information in these images can be analysed objectively and accurately using colour histograms. One such process is olive ripening, which is characterized by changes in chemical composition, sensory properties and can be followed by changes in physical appearance, mainly colour. The reference method to quantify the ripeness of olives is the Maturity Index (MI), which is determined by trained experts assigning individual olives into a colour scale through visual inspection. Instead, this study proposes a methodology based on Chemometrics Assisted Colour Histogram-based Analytical Systems (CACHAS) to automatically assess the MI of olives based on R, G, and B colour histograms derived from digital images. The methodology was shown to be easily transferable for routine analysis and capable of controlling the ripening of olives. The study also confirms the high potential of digital images to understand the ripening process of olives (and potentially other fruits) and to predict the MI with satisfactory accuracy, providing an objective and reproducible alternative to visual inspection of trained experts.

Smartphone-enabled colorimetric visual quantification of highly hazardous trivalent chromium ions in environmental waters and catalytic reduction of p-nitroaniline by thiol-functionalized gold nanoparticles

High-efficiency sensing systems for extremely hazardous chromium (Cr(III)) ions are important due to their detrimental effects on human health and the environment. We employed a spectrophotometric method combined with a smartphone (red, green, and blue (RGB) color ratio)-based detection platform to realize the quick, visually quantifiable in situ detection of Cr(III) ions using surface plasmon resonance (SPR)-aided colorimetry. For optical sensing nanoprobes, we synthesized the 2-Mercapto-5-methyl-1,3,4-thiadiazole (MMT)-modified gold nanoparticles (MMT-AuNPs) using a wet chemical method. By way of a coordination reaction, the Cr(III) ions induce the as-prepared MMT-AuNPs to aggregate and subsequently change the SPR wavelength band. The freshly synthesized MMT-AuNPs exhibited a wine-red color. While Cr(III) ions interact with the MMT-AuNPs, the color of the latter evolved from wine red to purple, thus facilitating visual monitoring. The SPR-relevant color change allowed the quantitative sensing of Cr(III) ions in the range of 40-128 nM, with the limit of detection of 6.93 nM when employing the spectrophotometric method and 12.4 nM when using the smartphone RGB color ratio. Furthermore, we developed the spectrophotometric technique that used the smartphone RGB color ratio for on-site analysis of Cr(III) ions in environmental water samples, indicating the possibility of its chemo-sensing applications for portable quantitative detection devices. Additionally, the catalytic performance of the MMT-AuNPs was demonstrated by the reduction of p-nitroaniline in the presence of sodium borohydride. It was interestingly unveiled that the MMT-AuNPs showed outstanding catalytic performance with a catalytic rate constant of 6.31 × 10-3 s-1.

Toward Citizen Science-Based Ocean Acidification Observations Using Smartphone Devices

pH is a key parameter in many chemical, biological, and biogeochemical processes, making it a fundamental aspect of environmental monitoring. Rapid and accurate seawater pH measurements are essential for effective ocean observation and acidification investigations, resulting in the need for novel solutions that allow robust, precise, and affordable pH monitoring. In this study, a versatile smartphone-based environmental analyzer (vSEA) was used for the rapid measurement of seawater pH in a field study. The feasibility of the use of the vSEA algorithm for pH quantification was explored and verified. When used in conjunction with a three-dimensional (3D)-printed light-proof shell, the quality of captured images is guaranteed. The quantitative accuracy of vSEA pH measurements reached 0.018 units with an uncertainty of <0.01, meeting the requirements of the Global Ocean Acidification Observing Network (GOA-ON) for "weather" goals (permitting a maximum pH uncertainty of 0.02). The vSEA-pH system was successfully applied for on-site pH measurements in coastal seawater and coral systems. The performance of the vSEA-pH system was validated using different real-world samples, and t-test results showed that the vSEA-pH system was consistent with pH measurements obtained using a state-of-the-art benchtop spectrophotometer (t = 1.986, p = 0.7949). The vSEA-pH system is applicable to different types of smartphone devices, making it possible for vSEA-pH to be widely promoted for public citizen use. The vSEA-pH system offers a simple, accurate, and applicable method for the on-site measurement of seawater pH, assisting the large-scale monitoring of ocean acidification by allowing the contribution of citizen science-based data collection.

Rapid Point-of-Care Identification of Aspergillus Species in Microbial Keratitis

Importance

Microbial keratitis (MK) is a common cause of unilateral visual impairment, blindness, and eye loss in low-income and middle-income countries. There is an urgent need to develop and implement rapid and simple point-of-care diagnostics for MK to increase the likelihood of good outcomes.

Objective

To evaluate the diagnostic performance of the Aspergillus-specific lateral-flow device (AspLFD) to identify Aspergillus species causing MK in corneal scrape and corneal swab samples of patients presenting with microbial keratitis.

Design, Setting, and Participants

This diagnostic study was conducted between May 2022 and January 2023 at the corneal clinic of Aravind Eye Hospital in Madurai, Tamil Nadu, India. All study participants were recruited during their first presentation to the clinic. Patients aged 15 years or older met the eligibility criteria if they were attending their first appointment, had a corneal ulcer that was suggestive of a bacterial or fungal infection, and were about to undergo diagnostic scrape and culture.

Main Outcomes and Measures

Sensitivity and specificity of the AspLFD with corneal samples collected from patients with MK. During routine diagnostic scraping, a minimally invasive corneal swab and an additional corneal scrape were collected and transferred to aliquots of sample buffer and analyzed by lateral-flow device (LFD) if the patient met the inclusion criteria. Photographs of devices were taken with a smartphone and analyzed using a ratiometric approach, which was developed for this study. The AspLFD results were compared with culture reports.

Results

The 198 participants who met the inclusion criteria had a mean (range) age of 51 (15-85) years and included 126 males (63.6%). Overall, 35 of 198 participants with corneal scrape (17.7%) and 17 of 40 participants with swab samples (42.5%) had positive culture results for Aspergillus species. Ratiometric analysis results for the scrape samples found that the AspLFD achieved high sensitivity (0.89; 95% CI, 0.74-0.95), high negative predictive value (0.97; 95% CI, 0.94-0.99), low negative likelihood ratio (0.12; 95% CI, 0.05-0.30), and an accuracy of 0.94 (95% CI, 0.90-0.97). Ratiometric analysis results for the swab samples showed that the AspLFD had high sensitivity (0.94; 95% CI, 0.73-1.00), high negative predictive value (0.95; 95% CI, 0.76-1.00), low negative likelihood ratio (0.07; 95% CI, 0.01-0.48), and an accuracy of 0.88 (95% CI, 0.73-0.96).

Conclusions and Relevance

Results of this diagnostic study suggest that AspLFD along with the ratiometric analysis of LFDs developed for this study has high diagnostic accuracy in identifying Aspergillus species from corneal scrapes and swabs. This technology is an important step toward the provision of point-of-care diagnostics for MK and could inform the clinical management strategy.

Low-rate smartphone videoscopy for microsecond luminescence lifetime imaging with machine learning

Time-resolved techniques have been widely used in time-gated and luminescence lifetime imaging. However, traditional time-resolved systems require expensive lab equipment such as high-speed excitation sources and detectors or complicated mechanical choppers to achieve high repetition rates. Here, we present a cost-effective and miniaturized smartphone lifetime imaging system integrated with a pulsed ultraviolet (UV) light-emitting diode (LED) for 2D luminescence lifetime imaging using a videoscopy-based virtual chopper (V-chopper) mechanism combined with machine learning. The V-chopper method generates a series of time-delayed images between excitation pulses and smartphone gating so that the luminescence lifetime can be measured at each pixel using a relatively low acquisition frame rate (e.g. 30 frames per second [fps]) without the need for excitation synchronization. Europium (Eu) complex dyes with different luminescent lifetimes ranging from microseconds to seconds were used to demonstrate and evaluate the principle of V-chopper on a 3D-printed smartphone microscopy platform. A convolutional neural network (CNN) model was developed to automatically distinguish the gated images in different decay cycles with an accuracy of >99.5%. The current smartphone V-chopper system can detect lifetime down to ∼75 µs utilizing the default phase shift between the smartphone video rate and excitation pulses and in principle can detect much shorter lifetimes by accurately programming the time delay. This V-chopper methodology has eliminated the need for the expensive and complicated instruments used in traditional time-resolved detection and can greatly expand the applications of time-resolved lifetime technologies.

Universal Method Based on Layer-by-Layer Assembly for Aptamer-Based Sensors for Small-Molecule Detection

Development of a fast and accurate pesticide analysis system is a challenging task, as a large amount of commonly used pesticide has negative effects on humans' health. Detection of pesticide residues is crucial for food safety management and environmental protection. Aptamers─short single-stranded oligonucleotides (RNA or DNA) selected by aptamer selection method SELEX─can selectively bind to their target pesticide molecules with high affinity. Thus, in the present study, we developed an electrochemical biosensor based on aptamers to detect the commonly used pesticide, glyphosate. Carbon fibers were used as the platform to assemble polyelectrolyte layers with the incorporated aptamers selectively binding with glyphosate molecules for electrochemical detection. The best limit of detection of 0.3 μM was achieved at open-circuit potential measurements, which is comparable to the current need in detection of glyphosate. The developed method can be implemented into existing systems for the determination of pesticides on farms to control residual concentrations of glyphosate in soil and water.

A portable electrochemical immunosensor for ovarian cancer uses hierarchical microporous carbon material from waste coffee grounds

A simple label-free electrochemical immunosensor for ovarian cancer (OC) detection was developed using a hierarchical microporous carbon material fabricated from waste coffee grounds (WCG). The analysis method exploited near-field communication (NFC) and a smartphone-based potentiostat. Waste coffee grounds were pyrolyzed with potassium hydroxide and used to modify a screen-printed electrode. The modified screen-printed electrode was decorated with gold nanoparticles (AuNPs) to capture a specific antibody. The modification and immobilization processes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The sensor had an effective dynamic range of 0.5 to 50.0 U mL^-1 of cancer antigen 125 (CA125) tumor marker with a correlation coefficient of 0.9995. The limit of detection (LOD) was 0.4 U mL^-1. A comparison of the results obtained from human serum analysis with the proposed immunosensor and the results obtained from the clinical method confirmed the accuracy and precision of the proposed immunosensor.

Smartphone-based diagnostics for biosensing infectious human pathogens

The widespread usage of smartphones has made accessing vast troves of data easier for everyone. Smartphones are powerful, handy, and easy to operate, making them a valuable tool for improving public health through diagnostics. When combined with other devices and sensors, smartphones have shown potential for detecting, visualizing, collecting, and transferring data, enabling rapid disease diagnosis. In resource-limited settings, the user-friendly operating system of smartphones allows them to function as a point-of-care platform for healthcare and disease diagnosis. Herein, we critically reviewed the smartphone-based biosensors for the diagnosis and detection of diseases caused by infectious human pathogens, such as deadly viruses, bacteria, and fungi. These biosensors use several analytical sensing methods, including microscopic imaging, instrumental interface, colorimetric, fluorescence, and electrochemical biosensors. We have discussed the diverse diagnosis strategies and analytical performances of smartphone-based detection systems in identifying infectious human pathogens, along with future perspectives.

Dextran-Functionalized Super-nanoparticle Assemblies of Quantum Dots for Enhanced Cellular Immunolabeling and Imaging

Colloidal semiconductor quantum dots (QDs) are a popular material for applications in bioanalysis and imaging. Although individual QDs are bright, some applications benefit from the use of even brighter materials. One approach to achieve higher brightness is to form super-nanoparticle (super-NP) assemblies of many QDs. Here, we present the preparation, characterization, and utility of dextran-functionalized super-NP assemblies of QDs. Amphiphilic dextran was synthesized and used to encapsulate many hydrophobic QDs via a simple emulsion-based method. The resulting super-NP assemblies or "super-QDs" had hydrodynamic diameters of ca. 90-160 nm, were characterized at the ensemble and single-particle levels, had orders-of-magnitude superior brightness compared to individual QDs, and were non-blinking. Additionally, binary mixtures of red, green, and blue (RGB) colors of QDs were used to prepare super-QDs, including colors difficult to obtain from individual QDs (e.g., magenta). Tetrameric antibody complexes (TACs) enabled simple antibody conjugation for selective cellular immunolabeling and imaging with both an epifluorescence microscope and a smartphone-based platform. The technical limitations of the latter platform were overcome by the increased per-particle brightness of the super-QDs, and the super-QDs outperformed individual QDs in both cases. Overall, the super-QDs are a very promising material for bioanalysis and imaging applications where brightness is paramount.

Addressing the Silent Spread of Monkeypox Disease with Advanced Analytical Tools

Monkeypox disease is caused by a virus which belongs to the orthopoxvirus genus of the poxviridae family. This disease has recently spread out to several non-endemic countries. While some cases have been linked to travel from endemic regions, more recent infections are thought to have spread in the community without any travel links, raising the risks of a wider outbreak. This state of public health represents a highly unusual event which requires urgent surveillance. In this context, the opportunities and technological challenges of current bio/chemical sensors, nanomaterials, nanomaterial characterization instruments, and artificially intelligent biosystems collectively called "advanced analytical tools" are reviewed here, which will allow early detection, characterization, and inhibition of the monkeypox virus (MPXV) in the community and limit its expansion from endemic to pandemic. A summary of background information is also provided from biological and epidemiological perspective of monkeypox to support the scientific case for its holistic management using advanced analytical tools.

Digital Platform for Automatic Qualitative and Quantitative Reading of a Cryptococcal Antigen Point-of-Care Assay Leveraging Smartphones and Artificial Intelligence

Cryptococcosis is a fungal infection that causes serious illness, particularly in immunocompromised individuals such as people living with HIV. Point of care tests (POCT) can help identify and diagnose patients with several advantages including rapid results and ease of use. The cryptococcal antigen (CrAg) lateral flow assay (LFA) has demonstrated excellent performance in diagnosing cryptococcosis, and it is particularly useful in resource-limited settings where laboratory-based tests may not be readily available. The use of artificial intelligence (AI) for the interpretation of rapid diagnostic tests can improve the accuracy and speed of test results, as well as reduce the cost and workload of healthcare professionals, reducing subjectivity associated with its interpretation. In this work, we analyze a smartphone-based digital system assisted by AI to automatically interpret CrAg LFA as well as to estimate the antigen concentration in the strip. The system showed excellent performance for predicting LFA qualitative interpretation with an area under the receiver operating characteristic curve of 0.997. On the other hand, its potential to predict antigen concentration based solely on a photograph of the LFA has also been demonstrated, finding a strong correlation between band intensity and antigen concentration, with a Pearson correlation coefficient of 0.953. The system, which is connected to a cloud web platform, allows for case identification, quality control, and real-time monitoring.

Progression of Paper-Based Point-of-Care Testing toward Being an Indispensable Diagnostic Tool in Future Healthcare

Point-of-care (POC) diagnostics in particular focuses on the timely identification of harmful conditions close to the patients' needs. For future healthcare these diagnostics could be an invaluable tool especially in a digitalized or telemedicine-based system. However, while paper-based POC tests, with the most prominent example being the lateral flow assay (LFA), have been especially successful due to their simplicity and timely response, the COVID-19 pandemic highlighted their limitations, such as low sensitivity and ambiguous responses. This perspective discusses strategies that are currently being pursued to evolve such paper-based POC tests toward a superior diagnostic tool that provides high sensitivities, objective result interpretation, and multiplexing options. Here, we pinpoint the challenges with respect to (i) measurability and (ii) public applicability, exemplified with select cases. Furthermore, we highlight promising endeavors focused on (iii) increasing the sensitivity, (iv) multiplexing capability, and (v) objective evaluation to also ready the technology for integration with machine learning into digital diagnostics and telemedicine. The status quo in academic research and industry is outlined, and the likely highly relevant role of paper-based POC tests in future healthcare is suggested.

Smartphone surface plasmon resonance imaging for the simultaneous and sensitive detection of acute kidney injury biomarkers with noninvasive urinalysis

A surface plasmon resonance imaging (SPRi) platform integrated with a smartphone was constructed for the simultaneous and sensitive detection of acute kidney injury (AKI) biomarkers. The smartphone SPRi platform was developed without the requirement of additional light and power sources. The LED flash of the smartphone was used as the light source for the excitation of surface plasmon resonance of a gold sensor chip based on the Kretschmann configuration, while the reflected light was collected by the camera of the smartphone. This smartphone SPRi system was conveniently fabricated by 3D printing and showed a sensitivity of 1.78 × 10^-5 refractive index unit (RIU). In addition, based on a magnetic nanoparticle-enhanced sandwich immunoassay, the smartphone SPRi system with a gold array chip was employed for the detection of multiple AKI biomarkers, with a low limit of detection (LOD) of 0.19 ng ml^-1, 0.51 ng ml^-1 and 0.7 ng ml^-1 for the simultaneous detection of neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18 (IL-18) and retinol-binding protein (RBP) in urine, respectively. The biosensors demonstrated high specificity and sensitivity for the simultaneous detection of multiple AKI biomarkers in PBST and urine. The smartphone SPRi system provided a portable and cost-effective platform for point-of-care diagnosis, in-field healthcare and environmental monitoring.

Growth of Plasmonic Nanoparticles for Aging Cask-Matured Whisky

The maturation of spirit in wooden casks is key to the production of whisky, a hugely popular and valuable product, with the transfer and reaction of molecules from the wooden cask with the alcoholic spirit imparting color and flavor. However, time in the cask adds significant cost to the final product, requiring expensive barrels and decades of careful storage. Thus, many producers are concerned with what "age" means in terms of the chemistry and flavor profiles of whisky. We demonstrate here a colorimetric test for spirit "agedness" based on the formation of gold nanoparticles (NPs) by whisky. Gold salts were reduced by barrel-aged spirit and produce colored gold NPs with distinct optical properties. Information from an extinction profile, such as peak position, growth rate, or profile shape, was analyzed, and our assay output was correlated with measurements of the whisky sample makeup, assays for key functional groups, and spiking experiments to explore the mechanism in more detail. We conclude that age is not just a number, that the chemical fingerprint of key flavor compounds is a useful marker for determining whisky "age", and that our simple reduction assay could assist in defining the aged character of a whisky and become a useful future tool on the warehouse floor.

Modification of Cotton Fabric with Molecularly Imprinted Polymer-Coated Carbon Dots as a Sensor for 17 α-methyltestosterone

Molecularly imprinted polymers@ethylenediamine-modified carbon dots grafted on cotton fabrics (MIPs@EDA-CDs/CF) and smartphone-based fluorescence image analysis were proposed and used for the first time for the detection of 17 α-methyltestosterone (MT). The EDA-CDs were synthesized and grafted on cotton fabric before coating with the MIPs. The MIPs were synthesized using the MT as a template molecule, methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as a cross-linker, and azobisisobutyronitrile (AIBN) as an initiator. The MIPs@EDA-CDs/CF were characterized using FTIR, SEM-EDS, and RGB fluorescence imaging. The fluorescence images were also taken using a smartphone and the ImageJ program was used for RGB measurement. The Δ red intensity was linearly proportional to MT concentration in the range of 100 to 1000 μg/L (R2 = 0.999) with a detection limit of 44.4 μg/L and quantification limit of 134 μg/L. The MIPs@EDA-CDs/CF could be stored at 4 °C for a few weeks and could be reused twice. The proposed method could apply for the specific determination of MT in water and sediment samples along with satisfactory recoveries of 96–104% and an acceptable relative standard deviation of 1–6% at the ppb level.

Dual-Color Fluorescent Hydrogel Microspheres Combined with Smartphones for Visual Detection of Lactate

Since it is difficult for human eyes to distinguish between two identical colors with only <15% variation in brightness, mono-color fluorescent hydrogel microspheres have some limitations in the detection of lactate. Herein, we prepared novel dual-color fluorescent hydrogel microspheres, which can achieve hue transformation. Microspheres were prepared by introducing a fluorescent nanoparticle as the reference signal while CdTe QDs were used as the response signal. We used smartphones with image processing software to collect and analyze data. In this way, the signal of lactate was converted to RGB (red, green, and blue) values, which can be quantitatively read. Within 10 to 1500 μM, the R/G values of the microspheres had a linear relationship with the logarithm of the lactate concentration. Moreover, color cards for lactate detection were prepared, from which the color change and concentration of lactate could be easily read by the naked eye. It is worth mentioning that this method was successfully applied to screen patients with hyperlactatemia.

Excitation modalities for enhanced micro and nanoparticle imaging in a smartphone coupled 3D printed fluorescent microscope

Smartphone fluorescent microscopes (SFM) offer many functional characteristics similar to their benchtop counterparts at a fraction of the cost and have been shown to work for biomarker detection in many biomedical applications. However, imaging and quantification of bioparticles in the sub-micron and nanometer range remains challenging as it requires aggressive robustness and high-performance metrics of the building blocks of SFM. Here, we explored multiple excitation modalities and their performance on the imaging capability of an SFM. Employing spatial positional variations of the excitation source with respect to the imaging sample plane (i.e., parallel, perpendicular, oblique), we developed three distinct SFM variants. These SFM variants were tested using green-fluorescent beads of four different sizes (8.3, 2, 1, 0.8 μm). Optimal excitation voltage range was determined by imaging these beads at multiple excitation voltages to optimize for no data loss and acceptable noise levels for each SFM variant. The SFM with parallel excitation was able to only image 8.3 μm beads while the SFM variants with perpendicular and oblique excitation were able to image all four bead sizes. Relative performance of the SFM variants was quantified by calculating signal difference to noise ratio (SDNR) and contrast to noise ratio (CNR) from the captured images. SFM with oblique excitation generated the highest SDNR and CNR values, whereas, for power consumption, SFM with perpendicular excitation generated the best results. This study sheds light on significant findings related to performance of SFM systems and their potential utility in biomedical applications involving sub-micron imaging. Similarly, findings of this study are translatable to benchtop microscopy instruments as well as to enhance their imaging performance metrics.

Fluorescent sensor based on pyrroloquinoline quinone (PQQ)-glucose dehydrogenase for glucose detection with smartphone-adapted signal analysis

A new nano-structured platform for fluorescent analysis using PQQ-dependent glucose dehydrogenase (PQQ-GDH) was developed, particularly using a smartphone for transduction and quantification of optical signals. The PQQ-GDH enzyme was immobilized on SiO₂ nanoparticles deposited on glass microfiber filter paper, providing a high load of the biocatalytic enzyme. The platform was tested and optimized for glucose determination using a wild type of the PQQ-GDH enzyme. The analysis was based on the fluorescence generated by the reduced form of phenazine methosulfate produced stoichiometrically to the glucose concentration. The fluorescent signals were generated at separate analytical spots on the paper support under wavelength (365 nm) UV excitation. The images of the analytical spots, dependent on the glucose concentration, were obtained using a photo camera of a standard smartphone. Then, the images were processed and quantified using software installed in a smartphone. The developed biocatalytic platform is the first step to assembling a large variety of biosensors using the same platform functionalized with artificial allosteric chimeric PQQ-dependent glucose dehydrogenase activated with different analytes. The future combination of the artificial enzymes, the presently developed analytical platform, and signal processing with a smartphone will lead to novel point-of-care and end-user biosensors applicable to virtually all possible analytes.

Toward Next Generation Lateral Flow Assays: Integration of Nanomaterials

Lateral flow assays (LFAs) are currently the most used point-of-care sensors for both diagnostic (e.g., pregnancy test, COVID-19 monitoring) and environmental (e.g., pesticides and bacterial monitoring) applications. Although the core of LFA technology was developed several decades ago, in recent years the integration of novel nanomaterials as signal transducers or receptor immobilization platforms has brought improved analytical capabilities. In this Review, we present how nanomaterial-based LFAs can address the inherent challenges of point-of-care (PoC) diagnostics such as sensitivity enhancement, lowering of detection limits, multiplexing, and quantification of analytes in complex samples. Specifically, we highlight the strategies that can synergistically solve the limitations of current LFAs and that have proven commercial feasibility. Finally, we discuss the barriers toward commercialization and the next generation of LFAs.

Evaluating and mitigating clinical samples matrix effects on TX-TL cell-free performance

Cell-free biosensors are promising tools for medical diagnostics, yet their performance can be affected by matrix effects arising from the sample itself or from external components. Here we systematically evaluate the performance and robustness of cell-free systems in serum, plasma, urine, and saliva using two reporter systems, sfGFP and luciferase. In all cases, clinical samples have a strong inhibitory effect. Of the different inhibitors, only RNase inhibitor mitigated matrix effects. However, we found that the recovery potential of RNase inhibitor was partially muted by interference from glycerol contained in the commercial buffer. We solved this issue by designing a strain producing an RNase inhibitor protein requiring no additional step in extract preparation. Furthermore, our new extract yielded higher reporter levels than previous conditions and tempered interpatient variability associated with matrix effects. This systematic evaluation and improvements of cell-free system robustness unified across many types of clinical samples is a significant step towards developing cell-free diagnostics for a wide range of conditions.

Personal Digital Twin: A Close Look into the Present and a Step towards the Future of Personalised Healthcare Industry

Digital twins (DTs) play a vital role in revolutionising the healthcare industry, leading to more personalised, intelligent, and proactive healthcare. With the evolution of personalised healthcare, there is a significant need to represent a virtual replica for individuals to provide the right type of care in the right way and at the right time. Therefore, in this paper, we surveyed the concept of a personal digital twin (PDT) as an enhanced version of the DT with actionable insight capabilities. In particular, PDT can bring value to patients by enabling more accurate decision making and proper treatment selection and optimisation. Then, we explored the progression of PDT as a revolutionary technology in healthcare research and industry. However, although several research works have been performed for smart healthcare using DT, PDT is still at an early stage. Consequently, we believe that this work can be a step towards smart personalised healthcare industry by guiding the design of industrial personalised healthcare systems. Accordingly, we introduced a reference framework that empowers smart personalised healthcare using PDTs by bringing together existing advanced technologies (i.e., DT, blockchain, and AI). Then, we described some selected use cases, including the mitigation of COVID-19 contagion, COVID-19 survivor follow-up care, personalised COVID-19 medicine, personalised osteoporosis prevention, personalised cancer survivor follow-up care, and personalised nutrition. Finally, we identified further challenges to pave the PDT paradigm toward the smart personalised healthcare industry.

Bluetooth-Connected Pocket Spectrometer and Chemometrics for Olive Oil Applications

Unsaturated fatty acids are renowned for their beneficial effects on the cardiovascular system. The high content of unsaturated fatty acids is a benefit of vegetable fats and an important nutraceutical indicator. The ability to quickly check fat composition of an edible oil could be advantageous for both consumers and retailers. A Bluetooth-connected pocket spectrometer operating in NIR band was used for analyzing olive oils of different qualities. Reference data for fatty acid composition were obtained from a certified analytical laboratory. Chemometrics was used for processing data, and predictive models were created for determining saturated and unsaturated fatty acid content. The NIR spectrum also demonstrated good capability in classifying extra virgin and non-extra virgin olive oils. The pocket spectrometer used in this study has a relatively low cost, which makes it affordable for a wide class of users. Therefore, it may open the opportunity for quick and non-destructive testing of edible oil, which can be of interest for consumer, retailers, and for small/medium-size producers, which lack easy access to conventional analytics.

Microsecond-resolved smartphone time-gated luminescence spectroscopy

Time-gated luminescence spectra are usually measured by laboratory instruments equipped with high-speed excitation sources and spectrometers, which are always bulky and expensive. To reduce the reliance on expensive laboratory instruments, we demonstrate the first, to the best of our knowledge, use of a smartphone for the detection of time-gated luminescence spectra. A mechanical chopper is used as the detection shutter and an optical switch is placed at the edge of the wheel to convert the chopping signal into a transistor-transistor logic (TTL) signal which is used to control the excitation source and achieve synchronization. The time-gated luminescence spectra at different delay times of Eu(TTA)₃ powder and the solutions of Eu-tetracycline complex are successfully detected with a temporal resolution of tens of microseconds by the proposed approach. We believe our approach offers a route toward portable instruments for the measurement of luminescence spectra and lifetimes.

Emerging Bioanalytical Devices and Platforms for Rapid Detection of Pathogens in Environmental Samples

The development of robust bioanalytical devices and biosensors for infectious pathogens is progressing well with the advent of new materials, concepts, and technology. The progress is also stepping towards developing high throughput screening technologies that can quickly identify, differentiate, and determine the concentration of harmful pathogens, facilitating the decision-making process for their elimination and therapeutic interventions in large-scale operations. Recently, much effort has been focused on upgrading these analytical devices to an intelligent technological platform by integrating them with modern communication systems, such as the internet of things (IoT) and machine learning (ML), to expand their application horizon. This review outlines the recent development and applications of bioanalytical devices and biosensors to detect pathogenic microbes in environmental samples. First, the nature of the recent outbreaks of pathogenic microbes such as foodborne, waterborne, and airborne pathogens and microbial toxins are discussed to understand the severity of the problems. Next, the discussion focuses on the detection systems chronologically, starting with the conventional methods, advanced techniques, and emerging technologies, such as biosensors and other portable devices and detection platforms for pathogens. Finally, the progress on multiplex assays, wearable devices, and integration of smartphone technologies to facilitate pathogen detection systems for wider applications are highlighted.

A Universal Multichannel Platform for Assembling Enzyme-Based Boolean Logic Gates

Concatenated enzyme-based Boolean logic gates activated with 5 chemical input signals were analyzed with a smartphone photo camera. Simultaneous detection of 32 input combinations was conveniently performed using enzyme-modified fiberglass sensing spots generating fluorescence with different intensities for the 0 and 1 binary outputs. The developed technology offers an easy readout method for multi-channel logic systems.

Bipolar Electrode Arrays for Chemical Imaging and Multiplexed Sensing

Bipolar electrodes (BPEs) with arrays of cathodic and anodic poles were developed for use in closed bipolar systems. To increase the number of BPEs in the array, the anodic and cathodic poles were connected with each other using thin leads. A further increase in the number of BPEs was achieved by forming the cathodic and anodic poles of the BPEs and the leads in different layers. A device with 9 × 10 arrays of cathodes and anodes was thus realized. When using this device to sense hydrogen peroxide (H₂O₂), the sensitivity and linear range of calibration plots could be adjusted by changing the driving voltage and the area ratio between the cathodic and anodic poles. The devices were used to image H₂O₂ and obtain time-lapse images for the diffusion and dilution of H₂O₂. Furthermore, DNA detection was demonstrated using an electroactive intercalator. The sensitivity could be improved by making the anodic poles smaller with respect to the cathodic pole and concentrating the electrochemiluminescence (ECL) in a small area. The ECL intensity changed according to the target DNA concentration in the solution.