Multiplexed Homogeneous Assays of Proteolytic Activity Using a Smartphone and Quantum Dots

Supra-Quantum Dot Assemblies to Maximize Color-Based Multiplexed Fluorescence Detection with a Smartphone Camera

Photoluminescence (PL) imaging and bioanalysis with smartphone-based devices are of growing interest for point-of-care/point-of-need diagnostics. Strategies for maximizing sensitivity have been explored in this context, but color multiplexing has been very limited, with its maximum level unexplored. Here, we evaluated color multiplexing with smartphone-based PL imaging by using supra-nanoparticle assemblies of quantum dots (supra-QDs). These materials were prepared as composite colors that were tailored to the red-green-blue (RGB) color space of smartphone cameras by coassembling different ratios of R-, G-, and B-emitting QDs on a silica nanoparticle scaffold. The supra-QDs were characterized and used to label cell-sized objects that were measured under flow with a smartphone-based device. Each color followed an approximately linear trajectory in the RGB space, and training of support vector machine models enabled color classification with overall accuracies ≥87% for 10-color multiplexing and better accuracies for fewer colors. Most misclassification occurred at low signal levels, such that establishing a nonclassifiable zone near the origin of RGB color space improved the overall 10-color classification accuracy to ≥94%. Similar improvements in accuracy with greater retention of data were possible with a probabilistic rather than a radial threshold. Simulations that were parameterized by experimental data suggested that ≥14-color multiplexing with accuracies ≥90% should be possible with an optimized supra-QD color set. This study is an important foundation for advancing RGB color-based multiplexing for imaging and analyses with smartphone cameras and related charge-coupled device and CMOS color image sensor technologies.

Quantitative and Multiplexed Chopper-Based Time-Gated Imaging for Bioanalysis on a Smartphone

Smartphones are emerging platforms for point-of-care diagnostics (POCDs), where the on-board camera is, for example, used to image fluorescence. Many laboratory instruments are capable of time-gated (TG) photoluminescence (PL) measurements─an analytical method leveraged by multiple commercial assay kits. When paired with long-lived PL emitters such as luminescent lanthanide complexes (LLCs), time-gating eliminates background from sample autofluorescence and many other sources. This capability is amenable to minimally processed samples and would thus be useful for POCDs on a smartphone-based platform. Here, we report a double-chopper design for TG PL imaging using a portable, 3D-printed, smartphone-based device. The rotation speed, dimensions, and overlap of the chopper blades and gaps set the timing parameters, with delay times on the order of hundreds of microseconds to milliseconds. The device was capable of quantitative TG imaging of PL from terbium(III) and europium(III) LLCs, including rejection of short-lived PL background from serum and tissue phantoms, spectral and temporal multiplexing, a model time-gated Förster resonance energy transfer (TG-FRET) assay, and imaging of cells. As the first smartphone-based demonstrations of these important analytical capabilities, this work is an important foundation for developing POCD methods based on TG PL imaging.

Advances in paper based isothermal nucleic acid amplification tests for water-related infectious diseases

Water-associated or water-related infectious disease outbreaks are caused by pathogens such as bacteria, viruses, and protozoa, which can be transmitted through contaminated water sources, poor sanitation practices, or insect vectors. Low- and middle-income countries bear the major burden of these infections due to inadequate hygiene and subpar laboratory facilities, making it challenging to monitor and detect infections in a timely manner. However, even developed countries are not immune to these diseases, as inadequate wastewater management and contaminated drinking water supplies can also contribute to disease outbreaks. Nucleic acid amplification tests have proven to be effective for early disease intervention and surveillance of both new and existing diseases. In recent years, paper-based diagnostic devices have made significant progress and become an essential tool in detecting and managing water-associated diseases. In this review, we highlight the importance of paper and its variants as a diagnostic tool and discuss the properties, design modifications, and various paper-based device formats developed and used for detecting water-associated pathogens.

Accurate Identification of Mucinous Pancreatic Cystic Lesions Using Small-Volume Analytes

INTRODUCTION

The accurate identification of mucinous pancreatic cystic lesions (PCLs) is paramount for cancer risk stratification. Cyst fluid carcinoembryonic antigen (CEA), the only routinely used test, requires high volumes and has low sensitivity. We aimed to compare the performance of two investigational small-volume biomarkers, glucose and the protease gastricsin, to CEA for PCL classification.

METHODS

We obtained cyst fluid samples from 81 patients with pathologically confirmed PCLs from four institutions between 2003 and 2016. Gastricsin activity was measured using an internally quenched fluorescent substrate. Glucose levels were measured with a standard glucometer. CEA levels were obtained from the medical record. Models using Classification and Regression Trees were created to predict mucinous status. Model performance was evaluated using nested cross-validation.

RESULTS

Gastricsin activity, CEA, and glucose levels from patients with mucinous (n = 50) and nonmucinous (n = 31) PCLs were analyzed. Area under the curve (AUC) was similar for individual classifiers (gastricsin volume normalized [GVN] 0.88; gastricsin protein concentration normalized [GPN] 0.95; glucose 0.83; CEA 0.84). The combination of two classifiers did not significantly improve AUC, with CEA + GVN (0.88) performing similarly to CEA + GPN (0.95), GVN + glucose (0.87), GPN + glucose (0.95), and CEA + glucose (0.84). The three-analyte combination performed similarly to single and dual classifiers (GPN + glucose + CEA AUC 0.95; GVN + glucose + CEA AUC 0.87). After multiple comparison corrections, there were no significant differences between the individual, dual, and triple classifiers.

CONCLUSIONS

Gastricsin and glucose performed similarly to CEA and required <5% of the volume required for CEA; these classifiers may be useful in patients with limited cyst fluid. Future multicenter prospective studies are needed to validate and compare these novel small-volume biomarkers.

MicroLED biosensor with colloidal quantum dots and smartphone detection

A fluorescence sensor with the capability for spatially multiplexed measurements utilizing smartphone detection is presented. Bioconjugated quantum dots are used as the fluorescent tag and are excited using a blue-emitting microLED (µLED). The 1-dimensional GaN µLED array is butt-coupled to one edge of the glass slide to take advantage of total internal reflection fluorescence (TIRF) principles. The bioassays on the top surface of the glass waveguide are excited and the resultant fluorescence is detected with the smartphone. The red, green, and blue channels of the digital image are utilized to spectrally separate the excitation light from the fluorescence for analysis. Using a biotin-functionalized glass slide as proof of principle, we have shown that streptavidin conjugated quantum dots can be detected down to a concentration of 8 nM.

Luminescence Nanomaterials for Biosensing Applications

Due to their capabilities of immobilizing more bioreceptor parts with reduced volumes, nanomaterials have emerged as potential tools for increasing sensitivity to specific molecules. Furthermore, carbon nanotube, gold nanoparticles, polymer nanoparticles, semiconductor quantum dots, graphene, nano-diamonds and graphene are among the nanomaterials that are under investigation. Due to the fast development of such a field of research, review summarises the classification of biosensors using main receptors, and designing biosensors. Numerous studies have concentrated on the manipulation of Persistent luminescence nanoparticles (PLNPs) in biosensing, cell tracking, bioimaging, and cancer therapy due to the effective removal of the autofluorescence interferences from tissues and the ultra-long near-infrared afterglow emission. As luminescence has a unique optical property, it can be detected without constant external illumination, preventing autofluorescence and light dispersion through tissues. These successes sparked an increasing curiosity in creating novel PLNP kinds with desired superior properties and multiple purposes. In this review, we emphasize the most recent developments in biosensing, imaging, and image-guided therapy while summarizing the research on synthesis methods, bio applications, bio membrane modification and bio-safety of PLNPs. Finally, the remaining issues and difficulties are examined together with prospective future developments in the field of biomedical applications.

Hydroxymethylation-Specific Ligation-Mediated Single Quantum Dot-Based Nanosensors for Sensitive Detection of 5-Hydroxymethylcytosine in Cancer Cells

5-Hydroxymethylcytosine (5hmC) modification is a key epigenetic regulator of cellular processes in mammalian cells, and its misregulation may lead to various diseases. Herein, we develop a hydroxymethylation-specific ligation-mediated single quantum dot (QD)-based fluorescence resonance energy transfer (FRET) nanosensor for sensitive quantification of 5hmC modification in cancer cells. We design a Cy5-modified signal probe and a biotinylated capture probe for the recognition of specific 5hmC-containing genes. 5hmC in target DNA can be selectively converted by T4 β-glucosyltransferase to produce a glycosyl-modified 5hmC, which cannot be cleaved by methylation-insensitive restriction enzyme MspI. The glycosylated 5hmC DNA may act as a template to ligate a signal probe and a capture probe, initiating hydroxymethylation-specific ligation to generate large amounts of biotin-/Cy5-modified single-stranded DNAs (ssDNAs). The assembly of biotin-/Cy5-modified ssDNAs onto a single QD through streptavidin-biotin interaction results in FRET and consequently the generation of a Cy5 signal. The nanosensor is very simple without the need for bisulfite treatment, radioactive reagents, and 5hmC-specific antibodies. Owing to excellent specificity and high amplification efficiency of hydroxymethylation-specific ligation and near-zero background of a single QD-based FRET, this nanosensor can quantify 5hmC DNA with a limit of detection of 33.61 aM and a wider linear range of 7 orders of magnitude, and it may discriminate the single-nucleotide difference among 5hmC, 5-methylcytosine, and unmodified cytosine. Moreover, this nanosensor can distinguish as low as a 0.001% 5hmC DNA in complex mixtures, and it can monitor the cellular 5hmC level and discriminate cancer cells from normal cells, holding great potential in biomedical research and clinical diagnostics.

Recent Advances in Electrochemical Biosensors for the Detection of Salmonellosis: Current Prospective and Challenges

Salmonellosis is a major cause of foodborne infections, caused by Salmonella, posing a major health risk. It possesses the ability to infiltrate the food supply chain at any point throughout the manufacturing, distribution, processing or quality control process. Salmonella infection has increased severely and requires effective and efficient methods for early monitoring and detection. Traditional methods, such as real-time polymerase chain reaction and culture plate, consume a lot of time and are labor-intensive. Therefore, new quick detection methods for on-field applications are urgently needed. Biosensors provide consumer-friendly approaches for quick on-field diagnoses. In the last few years, there has been a surge in research into the creation of reliable and advanced electrochemical sensors for the detection of Salmonella strains in food samples. Electrochemical sensors provide extensive accuracy and reproducible results. Herein, we present a comprehensive overview of electrochemical sensors for the detection of Salmonella by focusing on various mechanisms of electrochemical transducer. Further, we explain new-generation biosensors (microfluidics, CRISPR- and IOT-based) for point-of care applications. This review also highlights the limitations of developing biosensors in Salmonella detection and future possibilities.

Prototype Smartphone-Based Device for Flow Cytometry with Immunolabeling via Supra-nanoparticle Assemblies of Quantum Dots

Methods for the detection, enumeration, and typing of cells are important in many areas of research and healthcare. In this context, flow cytometers are a widely used research and clinical tool but are also an example of a large and expensive instrument that is limited to specialized laboratories. Smartphones have been shown to have excellent potential to serve as portable and lower-cost platforms for analyses that would normally be done in a laboratory. Here, we developed a prototype smartphone-based flow cytometer (FC). This compact 3D-printed device incorporated a laser diode and a microfluidic flow cell and used the built-in camera of a smartphone to track immunofluorescently labeled cells in suspension and measure their color. This capability was enabled by high-brightness supra-nanoparticle assemblies of colloidal semiconductor quantum dots (SiO₂@QDs) as well as a support vector machine (SVM) classification algorithm. The smartphone-based FC device detected and enumerated target cells against a background of other cells, simultaneously and selectively counted two different cell types in a mixture, and used multiple colors of SiO₂@QD-antibody conjugates to screen for and identify a particular cell type. The potential limits of multicolor detection are discussed alongside ideas for further development. Our results suggest that innovations in materials and engineering should enable eventual smartphone-based FC assays for clinical applications.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.

Optical bio-sensing of DNA methylation analysis: an overview of recent progress and future prospects

DNA methylation as one of the most important epigenetic modifications has a critical role in regulating gene expression and drug resistance in treating diseases such as cancer. Therefore, the detection of DNA methylation in the early stages of cancer plays an essential role in disease diagnosis. The majority of routine methods to detect DNA methylation are very tedious and costly. Therefore, designing easy and sensitive methods to detect DNA methylation directly and without the need for molecular methods is a hot topic issue in bioscience. Here we provide an overview on the optical biosensors (including fluorescence, FRET, SERs, colorimetric) that have been applied to detect the DNA methylation. In addition, various types of labeled and label-free reactions along with the application of molecular methods and optical biosensors have been surveyed. Also, the effect of nanomaterials on the sensitivity of detection methods is discussed. Furthermore, a comprehensive overview of the advantages and disadvantages of each method are provided. Finally, the use of microfluidic devices in the evaluation of DNA methylation and DNA damage analysis based on smartphone detection has been discussed.

Here, we provide an overview on the optical biosensors (including fluorescence, FRET, SERs, colorimetric) that have been applied to detect the DNA methylation.

A fluorescence color card for point-of-care testing (POCT) and its application in simultaneous detection

Diabetes mellitus has received much attention because its complications include liver, kidney, eye, heart and cerebrovascular diseases. Thus, it would be highly significant to develop a rapid and efficient method for glucose detection in biological samples. In this work, a point-of-care testing (POCT) method of glucose detection was proposed using a standard colorimetric card for semi-quantitative determination patterns. In the prepared fluorescence color card for glucose, a good linear relationship was acquired by plotting the ratio of the grayscale value (I/I0) versus the logarithm of glucose concentration within 100.0 to 1000.0 μmol L-1, and the LOD of glucose detection was 1.1 μmol L-1. A large number of actual samples (30 serum and 7 urine) were analyzed and the results demonstrated that this method had good potential to be applied in the primary screening of diabetic patients. In addition, this method is universal and can be applied in the simultaneous detection of multiple small molecules. It provides a new strategy for the primary screening of multiple diseases simultaneously, which presents excellent application potential.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

Development and Application of Mobile Apps for Molecular Sensing: A Review

Modern smartphone-based sensing devices are generally standalone detection platforms that can transduce signals (via the built-in USB port, audio jack, or camera), perform analysis through mobile applications (apps), and display results on the screen/user interface. The advancement toward this ultimate form of on-site chemical analysis and point-of-care diagnosis is tied closely with the evolution of mobile technology. Previous reviews in the field mainly focused on the physical platforms while overlooking the role of mobile apps in such devices. There exist three general stages throughout the development: (1) early generation telemedicine, (2) mobile phone-assisted clinical diagnosis (without apps), and (3) mobile app-based sensing devices for various analytes. This review presents the key breakthroughs during each stage, recent development, remaining challenges, and future perspectives of the field. Representative examples, spanning from the pioneering point-of-care testing to the latest devices with integrated mobile apps, are classified by their sensing mechanisms. The review also discusses the scarcity of open-source apps dedicated to molecular sensing. With the introduction of more open-source and commercial apps, the mobile app-based detection system is anticipated to dominate point-of-care diagnosis and on-site molecular sensing in our opinion.

Smartphone-based optical analysis systems

During the past few decades, there has been a growing trend towards the use of smartphone-based analysis systems. This is mainly due to its ubiquity, its increasing computing capacity, its relatively low cost and the ability to acquire and process data at the same time. Furthermore, there are many sensors integrated into a smartphone, for example a complementary metal-oxide semiconductor (CMOS) sensor. A CMOS sensor enables optical analysis for example by using it as a colorimeter, photometer or spectrometer. This review explores the current state-of-the-art smartphone-based optical analysis systems in various areas of application. It is organized into three sections, each of which investigates one class of smartphone-based devices: (i) smartphone-based colorimeters (ii) smartphone-based photo- and spectrometers and (iii) smartphone-based fluorimeters.

Ratiometric Fluorescent Lateral Flow Immunoassay for Point-of-Care Testing of Acute Myocardial Infarction

We report the development of a highly sensitive ratiometric fluorescent lateral flow immunoassay (RFLFIA) strip for rapid and accurate detection of acute myocardial infarction biomarker, namely heart-type fatty acid binding protein (H-FABP). The RFLFIA strip works in terms of ratiometric change of fluorescence signal, arising from blending of fluorescence emitted by two composite nanostructures conjugated to capture and probe antibodies and inner filter effect of gold nanoparticles. In conjunction with using custom smartphone-based analytical device and tonality analysis, quantitative detection of H-FABP was achieved with a low limit of detection at 0.21 ng mL^-1 . The RFLFIA strip can generate a visually distinguishable green-to-red color change around the threshold concentration of H-FABP (6.2 ng mL^-1 ), thus allowing the semi-quantitative diagnosis by the naked eye.

Point-of-care testing (POCT) of patients with a high concentration of uric acid by using alginate hydrogel microspheres embedded with CdZnTeS QDs and urate oxidase (Alg@QDs-UOx MSs)

A more convenient method for POCT of patients with a high concentration of uric acid by using Alg@QDs-UOx MSs is developed.

Transcription Factor Based Small-Molecule Sensing with a Rapid Cell Phone Enabled Fluorescent Bead Assay

Recently, allosteric transcription factors (TFs) were identified as a novel class of biorecognition elements for in vitro sensing, whereby an indicator of the differential binding affinity between a TF and its cognate DNA exhibits dose-dependent responsivity to an analyte. Described is a modular bead-based biosensor design that can be applied to such TF-DNA-analyte systems. DNA-functionalized beads enable efficient mixing and spatial separation, while TF-labeled semiconductor quantum dots serve as bright fluorescent indicators of the TF-DNA bound (on bead) and unbound states. The prototype sensor for derivatives of the antibiotic tetracycline exhibits nanomolar sensitivity with visual detection of bead fluorescence. Facile changes to the sensor enable sensor response tuning without necessitating changes to the biomolecular affinities. Assay components self-assemble, and readout by eye or digital camera is possible within 5 minutes of analyte addition, making sensor use facile, rapid, and instrument-free.

Monitoring of reaction kinetics and determination of trace water in hydrophobic organic solvents by a smartphone-based ratiometric fluorescence device

A smartphone-based ratiometric fluorescence device was designed to monitor the reaction kinetic process under vigorous mixing conditions, demonstrated by the hydrolysis of Cs₄PbBr₆ nanocrystals (NCs). In the presence of trace water, part of Cs₄PbBr₆ NCs (non-fluorescent) was converted to CsPbBr₃ NCs (strong fluorescent). Using anthracene as the reference fluorophore, the brightness ratio of the green (from CsPbBr₃ NCs) to blue (from anthracene) components in the fluorescence image which was recorded in situ by the smartphone camera was measured as the signal for kinetic analysis. It was shown that the water-triggered conversion reaction from Cs₄PbBr₆ NCs to CsPbBr₃ NCs follows the pseudo-second-order kinetic model in the early rapid hydrolysis stage (up to 4 min). With increasing water content, the hydrolysis of Cs₄PbBr₆ NCs is promoted to yield more CsPbBr₃ NCs, which was used to determine trace water in n-hexane, dichloromethane, and toluene with detection limits of 0.031, 0.043, and 0.057 μL mL^-1, respectively. The device offers the advantages of portability and low cost for rapid field determination of trace water in hydrophobic organic solvents. Graphical abstract.

Quantum dot to quantum dot Förster resonance energy transfer: engineering materials for visual color change sensing

In this work, quantum dots (QDs) of various heterostructured compositions and shell thicknesses are used as Förster or fluorescence resonance energy transfer (FRET) donors and acceptors to optimize QD-QD FRET sensing through materials design. While several reports have highlighted the advantages of using QD-dye, rather than dye-dye, FRET in sensing applications, QD-QD FRET has lagged behind in development as a result of high background signal from direct acceptor excitation. However, in designing sensors for longitudinal studies, QD-dye sensors are limited by the photostability of the fluorescent dye. While fluorescence generally affords higher sensitivity than absorbance-based readouts, the instrumentation needed for detecting fluorescence can be expensive, motivating the development of sensors bright enough to be seen by eye or imaged with cheap consumer electronics. Harnessing the exceptional brightness of QDs, our study focuses on the development of QD-QD FRET pairs where color change is achieved for visual readout and instrument-free sensing. We demonstrate that bulk semiconductor material characteristics can be used to a priori predict and tailor the behavior of QD-QD FRET systems, and our findings show that it is possible to create QD donors that are brighter than their acceptors through concerted compositional and morphological choices in heterostructured QDs. This is significant for developing visual sensors, as we show that the most profound color change occurs when the direct acceptor emission is lower than that of the donor. Finally, the use of an optimal cadmium-free QD-QD FRET pair is presented in a pH sensor that shows a large range of pH-dependent color change with bright, instrument-free readout.

Human Neutrophil Elastase Activated Fluorescent Probe for Pulmonary Diseases Based on Fluorescence Resonance Energy Transfer Using CdSe/ZnS Quantum Dots

There is an increasing demand for effective noninvasive diagnosis against common pulmonary diseases, which are rising sharply due to the serious air pollution. Human neutrophil elastase (HNE), a typical protease highly involved in pulmonary inflammatory diseases and lung cancer, is a potential predictor for disease progression. Currently, few of the HNE-targeting probes are applicable in vivo due to the limitation in sensitivity and biocompatibility. Herein, we reported the achievement of in vitro detection and in vivo imaging of HNE by incorporating the HNE-specific peptide substrate, quantum dots (QDs), and organic dyes into the fluorescence resonance energy transfer (FRET) system. The refined nanoprobe, termed QDP, could specifically measure the HNE with excellent sensitivity of 7.15 pM in aqueous solution and successfully image the endogenous and exogenous HNE in living cells. In addition, this nanoprobe enabled HNE imaging in mouse models of lung cancer and acute lung injury, and the HNE activity at high temporal and spatial resolution was continuously monitored. Most importantly, QDP successfully discriminated the serums of patients with lung diseases from those of the healthy controls based on the HNE activity determination. Overall, this study demonstrates the advantages of a FRET-system-based nanoprobe in imaging performance and provides an applicable tool for in vivo HNE detection and pulmonary disease diagnosis.

A multifunctional DNA nanostructure based on multicolor FRET for nuclease activity assay

We develop a four-color fluorescent probe for ratiometric detection of multiple nucleases based on multistep fluorescence resonance energy transfer.

Construction of Tetrahedral DNA-Quantum Dot Nanostructure with the Integration of Multistep Förster Resonance Energy Transfer for Multiplex Enzymes Assay

Three-dimensional (3D) DNA scaffolds with well-defined structure and high controllability hold promising potentials for biosensing and drug delivery. However, most of 3D DNA scaffolds can detect only a single type of molecule with the involvement of complex logic operations. Herein, we develop a 3D DNA nanostructure with the capability of multiplexed detection by exploiting a multistep Förster resonance energy transfer (FRET). The tetrahedron-structured DNA is constructed by four oligonucleotide strands and is subsequently conjugated to a streptavidin-coated quantum dot (QD) to obtain a QD-Cy3-Texas Red-Cy5 tetrahedron DNA. This QD-Cy3-Texas Red-Cy5 tetrahedral DNA nanostructure has well-defined dye-to-dye spacing and high controllability for energy transfer between intermediary acceptors and terminal acceptors, enabling the generation of multistep FRET between the QD and three dyes (i.e., Cy3, Texas Red, and Cy5) for simultaneous detection of multiple endonucleases and methyltransferases even in complex biological samples as well as the screening of multiple enzyme inhibitors.

Sensing with photoluminescent semiconductor quantum dots

Fluorescent sensors benefit from high signal-to-noise and multiple measurement modalities, enabling a multitude of applications and flexibility of design. Semiconductor nanocrystal quantum dots (QDs) are excellent fluorophores for sensors because of their extraordinary optical properties. They have high thermal and photochemical stability compared to organic dyes or fluorescent proteins and are extremely bright due to their large molar cross-sections. In contrast to organic dyes, QD emission profiles are symmetric, with relatively narrow bandwidths. In addition, the size tunability of their emission color, which is a result of quantum confinement, make QDs exceptional emitters with high color purity from the ultra-violet to near infrared wavelength range. The role of QDs in sensors ranges from simple fluorescent tags, as used in immunoassays, to intrinsic sensors that utilize the inherent photophysical response of QDs to fluctuations in temperature, electric field, or ion concentration. In more complex configurations, QDs and biomolecular recognition moieties like antibodies are combined with a third component to modulate the optical signal via energy transfer. QDs can act as donors, acceptors, or both in energy transfer-based sensors using Förster resonance energy transfer (FRET), nanometal surface energy transfer (NSET), or charge or electron transfer. The changes in both spectral response and photoluminescent lifetimes have been successfully harnessed to produce sensitive sensors and multiplexed devices. While technical challenges related to biofunctionalization and the high cost of laboratory-grade fluorimeters have thus far prevented broad implementation of QD-based sensing in clinical or commercial settings, improvements in bioconjugation methods and detection schemes, including using simple consumer devices like cell phone cameras, are lowering the barrier to broad use of more sensitive QD-based devices.

Inorganic Complexes and Metal-Based Nanomaterials for Infectious Disease Diagnostics

Infectious diseases claim millions of lives each year. Robust and accurate diagnostics are essential tools for identifying those who are at risk and in need of treatment in low-resource settings. Inorganic complexes and metal-based nanomaterials continue to drive the development of diagnostic platforms and strategies that enable infectious disease detection in low-resource settings. In this review, we highlight works from the past 20 years in which inorganic chemistry and nanotechnology were implemented in each of the core components that make up a diagnostic test. First, we present how inorganic biomarkers and their properties are leveraged for infectious disease detection. In the following section, we detail metal-based technologies that have been employed for sample preparation and biomarker isolation from sample matrices. We then describe how inorganic- and nanomaterial-based probes have been utilized in point-of-care diagnostics for signal generation. The following section discusses instrumentation for signal readout in resource-limited settings. Next, we highlight the detection of nucleic acids at the point of care as an emerging application of inorganic chemistry. Lastly, we consider the challenges that remain for translation of the aforementioned diagnostic platforms to low-resource settings.

Smartphone-based fluorescent lateral flow immunoassay platform for highly sensitive point-of-care detection of Zika virus nonstructural protein 1

Simple, inexpensive, and rapid diagnostic tests in low-resource settings with limited laboratory equipment and technical expertise are instrumental in reducing morbidity and mortality from epidemic infectious diseases. We developed a smartphone-based fluorescent lateral flow immunoassay (LFIA) platform for the highly sensitive point-of-care detection of Zika virus nonstructural protein 1 (ZIKV NS1). An attachment was designed and 3D-printed to integrate the smartphone with external optical and electrical components, enabling the miniaturization of the instrument and reduction in cost and complexity. Quantum dot microspheres were utilized as probes in fluorescent LFIA because of their extremely bright fluorescence signal. This approach can achieve quantitative point-of-care detection of ZIKV NS1 within 20 min. Limits of detection (LODs) in buffer and serum were 0.045 and 0.15 ng mL^-1, respectively. Despite the high structural similarity, a high-level Dengue virus NS1 as interferent showed limited cross-reactivity. Furthermore, this assay was successfully applied to detecte ZIKV NS1 and virions spiked in complex biological samples, indicating its practical application capability. Given its low cost, compact size, and excellent analytical performance, the proposed smartphone-based fluorescent LFIA platform holds considerable potential in rapid and accurate point-of-care detection of ZIKV NS1 and provides new insight into the design and application of molecular diagnostic methods in low-resource settings.

"The Smartphone's Guide to the Galaxy": In Situ Analysis in Space

A human mission to Mars can be viewed as the apex of human technological achievement. However, to make this dream a reality several obstacles need to be overcome. One is devising practical ways to safeguard the crew health during the mission through the development of easy operable and compact sensors. Lately, several smartphone-based sensing devices (SBDs) with the purpose to enable the immediate sensitive detection of chemicals, proteins or pathogens in remote settings have emerged. In this critical review, the potential to piggyback these systems for in situ analysis in space has been investigated on application of a systematic keyword search whereby the most relevant articles were examined comprehensively and existing SBDs were divided into 4 relevant groups for the monitoring of crew health during space missions. Recently developed recognition elements (REs), which could offer the enhanced ability to tolerate those harsh conditions in space, have been reviewed with recommendations offered. In addition, the potential use of cell free synthetic biology to obtain long-term shelf-stable reagents was reviewed. Finally, a synopsis of the possibilities of combining novel SBD, RE and nanomaterials to create a compact sensor-platform ensuring adequate crew health monitoring has been provided.

An Electrochemical Cholesterol Biosensor Based on A CdTe/CdSe/ZnSe Quantum Dots-Poly (Propylene Imine) Dendrimer Nanocomposite Immobilisation Layer

We report the preparation of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) as a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The mercaptopropionic acid (MPA)-capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray power diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima of the QDs red shifted as the reaction time and shell growth increased, indicating the formation of CdTe/CdSe/ZnSe QDs. PPI was electrodeposited on a glassy carbon electrode followed by the deposition (by deep coating) attachment of the QDs onto the PPI dendrimer modified electrode using 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS) as a coupling agent. The biosensor was prepared by incubating the PPI/QDs modified electrode into a solution of cholesterol oxidase (ChOx) for 6 h. The modified electrodes were characterized by voltammetry and impedance spectroscopy. Since efficient electron transfer process between the enzyme cholesterol oxidase (ChOx) and the PPI/QDs-modified electrode was achieved, the cholesterol biosensor (GCE/PPI/QDs/ChOx) was able to detect cholesterol in the range 0.1⁻10 mM with a detection limit (LOD) of 0.075 mM and sensitivity of 111.16 μA mM-1 cm-2. The biosensor was stable for over a month and had greater selectivity towards the cholesterol molecule.

Time-resolved and temperature tuneable measurements of fluorescent intensity using a smartphone fluorimeter

A smartphone fluorimeter capable of time-based fluorescence intensity measurements at various temperatures is reported. Excitation is provided by an integrated UV LED (λ_ex = 370 nm) and detection obtained using the in-built CMOS camera. A Peltier is integrated to allow measurements of the intensity over T = 10 to 40 °C. All components are controlled using a smartphone battery powered Arduino microcontroller and a customised Android application that allows sequential fluorescence imaging and quantification every δt = 4 seconds. The temperature dependence of fluorescence intensity for four emitters (rhodamine B, rhodamine 6G, 5,10,15,20-tetraphenylporphyrin and 6-(1,4,8,11-tetraazacyclotetradecane)2-ethyl-naphthalimide) are characterised. The normalised fluorescence intensity over time of the latter chemosensor dye complex in the presence of Zn²⁺ is observed to accelerate with an increasing rate constant, k = 1.94 min^-1 at T = 15 °C and k = 3.64 min^-1 at T = 30 °C, approaching a factor of ∼2 with only a change in temperature of ΔT = 15 °C. Thermally tuning these twist and bend associated rates to optimise sensor approaches and device applications is proposed.

Mobile Phone Ratiometric Imaging Enables Highly Sensitive Fluorescence Lateral Flow Immunoassays without External Optical Filters

Paper-based diagnostic tests based on the lateral flow immunoassay concept promise low-cost, point-of-care detection of infectious diseases, but such assays suffer from poor limits of detection. One factor that contributes to poor analytical performance is a reliance on low-contrast chromophoric optical labels such as gold nanoparticles. Previous attempts to improve the sensitivity of paper-based diagnostics include replacing chromophoric labels with enzymes, fluorophores, or phosphors at the expense of increased fluidic complexity or the need for device readers with costly optoelectronics. Several groups, including our own, have proposed mobile phones as suitable point-of-care readers due to their low cost, ease of use, and ubiquity. However, extant mobile phone fluorescence readers require costly optical filters and were typically validated with only one camera sensor module, which is inappropriate for potential point-of-care use. In response, we propose to couple low-cost ultraviolet light-emitting diodes with long Stokes-shift quantum dots to enable ratiometric mobile phone fluorescence measurements without optical filters. Ratiometric imaging with unmodified smartphone cameras improves the contrast and attenuates the impact of excitation intensity variability by 15×. Practical application was shown with a lateral flow immunoassay for influenza A with nucleoproteins spiked into simulated nasal matrix. Limits of detection of 1.5 and 2.6 fmol were attained on two mobile phones, which are comparable to a gel imager (1.9 fmol), 10× better than imaging gold nanoparticles on a scanner (18 fmol), and >2 orders of magnitude better than gold nanoparticle-labeled assays imaged with mobile phones. Use of the proposed filter-free mobile phone imaging scheme is a first step toward enabling a new generation of highly sensitive, point-of-care fluorescence assays.

Integration of isothermal amplification with quantum dot-based fluorescence resonance energy transfer for simultaneous detection of multiple microRNAs

The integration of quantum dot-based fluorescence resonance energy transfer with rolling circle amplification enables simultaneous sensitive detection of multiple microRNAs.

MicroRNAs (miRNAs) are small non-coding RNAs that regulate important physiological processes, and their dysregulation is associated with various human diseases. Simultaneous sensitive detection of multiple miRNAs may facilitate early clinical diagnosis. In this research, we demonstrate for the first time the integration of hyperbranched rolling circle amplification (HRCA) with quantum dot (QD)-based fluorescence resonance energy transfer (FRET) for the simultaneous detection of multiple microRNAs with a single-color QD as the donor and two fluorescent dyes as the acceptors. We used miR-21 and miR-221 as target miRNAs. We designed two circular templates which may specifically hybridize with miR-21 and miR-221, respectively, for the initiation of the HRCA reaction. The products of the HRCA reaction may hybridize with both capture probes and reporter probes to form the biotinylated acceptor-labeled sandwich hybrids. The resultant sandwich hybrids can assemble on the surface of the QD, enabling efficient FRET between the QD and the acceptors, with the Cy3 signal indicating the presence of miR-21 and the Texas Red signal indicating the presence of miR-221. This assay has significant advantages of simplicity and low cost. The HRCA reaction can be performed under isothermal conditions with the same reverse primer for different target miRNAs, and the products of the HRCA reaction for both miR-21 and miR-221 can specifically hybridize with the same capture probes. This assay exhibits excellent specificity and high sensitivity with a detection limit of 7.2 × 10^–16 M for miR-21 and 1.6 × 10^–17 M for miR-221, and it can be used for simultaneous detection of multiple miRNAs in human cancer cells, holding great potential in biomedical research and clinical diagnosis.

Culture-free, highly sensitive, quantitative detection of bacteria from minimally processed samples using fluorescence imaging by smartphone

A critical unmet need in the diagnosis of bacterial infections, which remain a major cause of human morbidity and mortality, is the detection of scarce bacterial pathogens in a variety of samples in a rapid and quantitative manner. Herein, we demonstrate smartphone-based detection of Staphylococcus aureus in a culture-free, rapid, quantitative manner from minimally processed liquid samples using aptamer-functionalized fluorescent magnetic nanoparticles. The tagged S. aureus cells were magnetically captured in a detection cassette, and then fluorescence was imaged using a smartphone camera with a light-emitting diode as the excitation source. Our results showed quantitative detection capability with a minimum detectable concentration as low as 10 cfu/ml by counting individual bacteria cells, efficiently capturing S. aureus cells directly from a peanut milk sample within 10 min. When the selectivity of detection was investigated using samples spiked with other pathogenic bacteria, no significant non-specific detection occurred. Furthermore, strains of S. aureus from various origins showed comparable results, ensuring that the approach can be widely adopted. Therefore, the quantitative fluorescence imaging platform on a smartphone could allow on-site detection of bacteria, providing great potential assistance during major infectious disease outbreaks in remote and resource-limited settings.

A smartphone-based double-channel fluorescence setup for immunoassay of a carcinoembryonic antigen using CuS nanoparticles for signal amplification

Sensitive detection of cancer biomarkers is valuable for clinical diagnosis and treatment assessment of cancers.

A selective colorimetric sensing strategy for cysteine based on an indicator-displacement mechanism

Rapid determination of cysteine in aqueous solution is important for the diagnosis and treatment of some diseases.

Development of quantum dot-based biosensors: principles and applications

We review the recent advances in quantum dot-based biosensors and focus on quantum dot-based fluorescent, bioluminescent, chemiluminescent, and photoelectrochemical biosensors.

Genome-wide host RNA signatures of infectious diseases: discovery and clinical translation

The use of whole blood gene expression to derive diagnostic biomarkers capable of distinguishing between phenotypically similar diseases holds great promise but remains a challenge. Differential gene expression analysis is used to identify the key genes that undergo changes in expression relative to healthy individuals, as well as to patients with other diseases. These key genes can act as diagnostic, prognostic and predictive markers of disease. Gene expression ‘signatures’ in the blood hold the potential to be used for the diagnosis of infectious diseases, where current diagnostics are unreliable, ineffective or of limited potential. For diagnostic tests based on RNA signatures to be useful clinically, the first step is to identify the minimum set of gene transcripts that accurately identify the disease in question. The second requirement is rapid and cost‐effective detection of the gene expression levels. Signatures have been described for a number of infectious diseases, but ‘clinic‐ready’ technologies for RNA detection from clinical samples are limited, though existing methods such as RT‐PCR are likely to be superseded by a number of emerging technologies, which may form the basis of the translation of gene expression signatures into routine diagnostic tests for a range of disease states.

A low-cost and miniaturized potentiostat for sensing of biomolecular species such as TNF-α by electrochemical impedance spectroscopy

Miniaturizing potentiostats, keeping their cost low and yet preserving full measurement characteristics (e.g. bandwidth, determination of capacitive/inductive contribution to sensor's impedance and parallel screening) is still an unresolved challenge in bioelectronics. In this work, the combination of simple analogue circuitry together with powerful microcontrollers and a digital filter implementation is presented as an alternative to complex and incomplete architectures reported in the literature. A low-cost acquisition electronic system fully integrated with a biosensors platform containing eight gold working microelectrodes and integrated reference and counter electrodes was developed and validated. The manufacturing cost of the prototype was kept below 300 USD. The performance of the proposed device was benchmarked against a commercial impedance analyzer through the electrochemical analysis of a highly sensitive biosensor for the detection of tumor necrosis factor α (TNF-α) within the randomly chosen range of 266pg/mL to 666ng/mL in physiological medium (PBS). A strong correlation between the outputs of both devices was found in a critical range of frequencies (1-10Hz), and several TNF-α cytokine concentrations were properly discriminated. These results are very promising for the development of low-cost, portable and miniaturized electrochemical systems for point-of-care and environmental diagnosis.