Rapid point-of-care detection of SARS-CoV-2 RNA with smartphone-based upconversion luminescence diagnostics

Advances and Opportunities of luminescence Nanomaterial for bioanalysis and diagnostics

Luminescence nanomaterials (LNMs) have recently received great attention in biological analysis and sensing owing to their key advances in easy design and functionalization with high photostability, luminescence stability, low autofluorescence, and multiphoton capacity. The number of publications surrounding LNMs for biological applications has grown rapidly. LNMs based on Stokes and anti-Stokes shifts are powerful tools for biological analysis. Especially, unique properties of anti-Stokes luminescence such as upconversion nanoparticles (UCNPs) with an implementation strategy to use longer-wavelength excitation sources such as near-infrared (NIR) light can depth penetrate to biological tissue for bioanalysis and bioimaging. We observed that the LNMs-based metal-organic frameworks (MOFs) have been developed and paid attention to the field of bioimaging and luminescence-based sensors, because of their structural flexibility, and multifunctionality for the encapsulation of luminophores. This article provides an overview of innovative LNMs such as quantum dots (QDs), UCNPs, and LMOFs. A brief summary of recent progress in design strategies and applications of LNMs including pH and temperature sensing in biologically responsive platforms, pathogen detection, molecular diagnosis, bioimaging, photodynamic, and radiation therapy published within the past three years is highlighted. It was found that the integrated nanosystem of lab-on-a-chip (LOC) with nanomaterials was rapidly widespread and erupting in interest after the COVID-19 pandemic. The simple operation and close processes of the integration nanosystem together with the optimized size and low energy and materials consumption of biochips and devices allow their trend study and application to develop portable and intelligent diagnostics tools. The last part of this work is the introduction of the utilization use of LNMs in LOC applications in terms of microfluidics and biodevices.

Recent advancements of smartphone-based sensing technology for diagnosis, food safety analysis, and environmental monitoring

The emergence of computationally powerful smartphones, relatively affordable high-resolution camera, drones, and robotic sensors have ushered in a new age of advanced sensible monitoring tools. The present review article investigates the burgeoning smartphone-based sensing paradigms, including surface plasmon resonance (SPR) biosensors, electrochemical biosensors, colorimetric biosensors, and other innovations for modern healthcare. Despite the significant advancements, there are still scarcity of commercially available smart biosensors and hence need to accelerate the rates of technology transfer, application, and user acceptability. The application/necessity of smartphone-based biosensors for Point of Care (POC) testing, such as prognosis, self-diagnosis, monitoring, and treatment selection, have brought remarkable innovations which eventually eliminate sample transportation, sample processing time, and result in rapid findings. Additionally, it articulates recent advances in various smartphone-based multiplexed bio sensors as affordable and portable sensing platforms for point-of-care devices, together with statistics for point-of-care health monitoring and their prospective commercial viability.

Microfluidic Chip-Assisted Upconversion Luminescence Biosensing Platform for Point-of-Care Virus Diagnostics

Epidemics caused by multiple viruses continue to emerge, which have brought a terrible impact on human society. Identification of viral infections with high sensitivity and portability is of significant importance for the screening and management of diseases caused by viruses. Herein, a microfluidic chip (MFC)-assisted upconversion luminescence biosensing platform is designed and fabricated for point-of-care virus detection. Upconversion nanoparticles with excellent stability are successfully synthesized as luminescent agents for optical signal generation in the portable virus diagnostic platform. The relevant investigation results illustrate that the MFC-assisted virus diagnostic platform possesses outstanding performance such as good integration, high sensitivity (1.12 pg mL-1), ease of use, and portability. In addition, clinical sample test result verifies its more prominent virus diagnostic properties than commercially available rapid test strips. All of these thrilling capabilities imply that the designed portable virus diagnostic platform has great potential for future virus detection applications.

Magnetic-responsive upconversion luminescence resonance energy transfer (LRET) biosensor for ultrasensitive detection of SARS-CoV-2 spike protein

Upconversion nanoparticles (UCNPs) are ideal donors for luminescence resonance energy transfer (LRET)-based biosensors due to their excellent upconversion luminescence properties. However, the relatively large size of antibodies and proteins limits the application of UCNPs-based LRET biosensors in protein detection because the large steric hindrance of proteins leads to low energy transfer efficiency between UCNPs and receptors. Herein, we developed a magnetic responsive UCNPs-based LRET biosensor to control the coupling distance between antibody-functionalized UCNPs (Ab-UCNPs) as donors and antibody-PEG linker-magnetic gold nanoparticles (Ab-PEG-MGNs) as acceptors for ultrasensitive and highly selective detection of SARS-CoV-2 spike proteins. Our results showed that this platform reversibly shortened the coupling distance between UCNPs and MGNs and enhanced the LRET signal with a 10-fold increase in the limit of detection (LOD) from 20.6 pg/mL without magnetic modulation to 2.1 pg/mL with magnetic modulation within 1 h. The finite-difference time-domain (FDTD) simulation with cyclic distance change confirmed the distance-dependent LRET efficiency under magnetic modulation, which supported the experimental results. Moreover, the applications of this magnetic-responsive UCNP-based LRET biosensor could be extended to other large-size biomolecule detection.

Biporous silica nanostructure-induced nanovortex in microfluidics for nucleic acid enrichment, isolation, and PCR-free detection

Efficient pathogen enrichment and nucleic acid isolation are critical for accurate and sensitive diagnosis of infectious diseases, especially those with low pathogen levels. Our study introduces a biporous silica nanofilms-embedded sample preparation chip for pathogen and nucleic acid enrichment/isolation. This chip features unique biporous nanostructures comprising large and small pore layers. Computational simulations confirm that these nanostructures enhance the surface area and promote the formation of nanovortex, resulting in improved capture efficiency. Notably, the chip demonstrates a 100-fold lower limit of detection compared to conventional methods used for nucleic acid detection. Clinical validations using patient samples corroborate the superior sensitivity of the chip when combined with the luminescence resonance energy transfer assay. The enhanced sample preparation efficiency of the chip, along with the facile and straightforward synthesis of the biporous nanostructures, offers a promising solution for polymer chain reaction-free detection of nucleic acids.

Revolutionizing SARS-CoV-2 omicron variant detection: Towards faster and more reliable methods

The emergence of the highly contagious Omicron variant of SARS-CoV-2 has inflicted significant damage during the ongoing COVID-19 pandemic. This new variant's significant sequence changes and mutations in both proteins and RNA have rendered many existing rapid detection methods ineffective in identifying it accurately. As the world races to control the spread of the virus, researchers are urgently exploring new diagnostic strategies to specifically detect Omicron variants with high accuracy and sensitivity. In response to this challenge, we have compiled a comprehensive overview of the latest reported rapid detection techniques. These techniques include strategies for the simultaneous detection of multiple SARS-CoV-2 variants and methods for selectively distinguishing Omicron variants. By categorizing these diagnostic techniques based on their targets, which encompass protein antigens and nucleic acids, we aim to offer a comprehensive understanding of the utilization of various recognition elements in identifying these targets. We also highlight the advantages and limitations of each approach. Our work is crucial in providing a more nuanced understanding of the challenges and opportunities in detecting Omicron variants and emerging variants.

Simple and Multiplexed Detection of Nucleic Acid Targets Based on Fluorescent Ring Patterns and Deep Learning Analysis

Simple diagnostic tests for nucleic acid targets can provide great advantages for applications such as rapid pathogen detection. Here, we developed a membrane assay for multiplexed detection of nucleic acid targets based on the visualization of two-dimensional fluorescent ring patterns. A droplet of the assay solution is applied to a cellulose nitrate membrane, and upon radial chromatographic flow and evaporation of the solvent, fluorescent patterns appear under UV irradiation. The target nucleic acid is isothermally amplified and is immediately hybridized with fluorescent oligonucleotide probes in a one-pot reaction. We established the fluorescent ring assay integrated with isothermal amplification (iFluor-RFA = isothermal fluorescent ring-based radial flow assay), and feasibility was tested using nucleic acid targets of the receptor binding domain (RBD) and RNA-dependent RNA polymerase (RdRp) genes of SARS-CoV-2. We demonstrate that the iFluor-RFA method is capable of specific and sensitive detection in the subpicomole range, as well as multiplexed detection even in complex solutions. Furthermore, we applied deep learning analysis of the fluorescence images, showing that patterns could be classified as positive or negative and that quantitative amounts of the target could be predicted. The current technique, which is a membrane pattern-based nucleic acid assay combined with deep learning analysis, provides a novel approach in diagnostic platform development that can be versatilely applied for the rapid detection of infectious pathogens.

Attomolar-level detection of respiratory virus long-chain oligonucleotides based on FRET biosensor with upconversion nanoparticles and Au-Au dimer

Upconversion nanoparticles (UCNPs) are promising nanoprobes in DNA/RNA detection, such as respiratory viral RNAs, and siRNA in cancer. However, recent studies have indicated that the sensitivity of UCNP-based biosensors is restricted, ranging from picomolar to femtomolar level. Moreover, most of existing UCNP-based probes are only able to detect short-chain oligonucleotides, which are not suitable for detection of long-chain oligonucleotides in many real applications. In this work, we introduced a new UCNP-based fluorescence resonance energy transfer (FRET) nanoprobe design composed of NaGdF4:Yb3+, Er3+@NaGdF4 core-shell UCNPs (csUCNPs) linking with Au-Au dimer to detect long-chain oligonucleotides of SARS-CoV-2 N-gene. Compared with typical single gold nanoparticles (AuNPs) in FRET biosensors, our theoretical investigation shows that a stronger electromagnetic field is generated in the Au-Au dimer where the plasmon resonance can enhance FRET efficiency and increase the working distance. Thus, the synergetic effect of plasmonic resonance and FRET enables a greater quenching efficiency (QE) of Au-Au dimer to UCNPs, which leads to more remarkable upconversion luminescence (UCL) recovery for each target gene recognition. Importantly, our design significantly improved the limit of detection (LOD) to attomolar level, with a linear response ranging from 2 aM to 2 fM. Moreover, the clinical detection with inactivated SARS-CoV-2 samples was successfully performed with excellent specificity within 30 min using the developed UCNPs biosensors incorporated with Au-Au dimer. This UCNP biosensor based on Au-Au dimer strategy with ultra-sensitivity and good selectivity opens a new path for clinical diagnosis without target amplification and plays an instructive role in other virus diagnosis.

PCR-Free Innovative Strategies for SARS-CoV-2 Detection

The pandemic outbreak caused by SARS-CoV-2 coronavirus brought a crucial issue in public health causing up to now more than 600 million infected people and 6.5 million deaths. Conventional diagnostic methods are based on quantitative reverse transcription polymerase chain reaction (RT-qPCR assay) and immuno-detection (ELISA assay). However, despite these techniques have the advantages of being standardized and consolidated, they keep some main limitations in terms of accuracy (immunoassays), time/cost consumption of analysis, the need for qualified personnel, and lab constrain (molecular assays). There is crucial the need to develop new diagnostic approaches for accurate, fast and portable viral detection and quantification. Among these, PCR-free biosensors represent the most appealing solution since they can allow molecular detection without the complexity of the PCR. This will enable the possibility to be integrated in portable and low-cost systems for massive and decentralized screening of SARS-CoV-2 in a point-of-care (PoC) format, pointing to achieve a performant identification and control of infection. In this review, the most recent approaches for the SARS-CoV-2 PCR-free detection are reported, describing both the instrumental and methodological features, and highlighting their suitability for a PoC application.

Development of a loop-mediated isothermal amplification (LAMP)-based electrochemical test for rapid detection of SARS-CoV-2

Rapid, reliable, sensitive, portable, and accurate diagnostics are required to control disease outbreaks such as COVID-19 that pose an immense burden on human health and the global economy. Here we developed a loop-mediated isothermal amplification (LAMP)-based electrochemical test for the detection of SARS-CoV-2 that causes COVID-19. The test is based on the oxidation-reduction reaction between pyrophosphates (generated from positive LAMP reaction) and molybdate that is detected by cyclic voltammetry using inexpensive and disposable carbon screen printed electrodes. Our test showed higher sensitivity (detecting as low as 5.29 RNA copies/μL) compared to the conventional fluorescent reverse transcriptase (RT)-LAMP. We validated our tests using human serum and saliva spiked with SARS-CoV-2 RNA and clinical (saliva and nasal-pharyngeal) swab samples demonstrating 100% specificity and 93.33% sensitivity. Our assay provides a rapid, specific, and sensitive test with an electrochemical readout in less than 45 min that could be adapted for point-of-care settings.

Smartphone-based point-of-care testing of the SARS-CoV-2: A systematic review

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus's worldwide pandemic has highlighted the urgent need for reliable, quick, and affordable diagnostic tests for comprehending and controlling the epidemic by tracking the world population. Given how crucial it is to monitor and manage the pandemic, researchers have recently concentrated on creating quick detection techniques. Although PCR is still the preferred clinical diagnostic test, there is a pressing need for substitutes that are sufficiently rapid and cost-effective to provide a diagnosis at the time of use. The creation of a quick and simple POC equipment is necessary for home testing. Our review's goal is to provide an overview of the many methods utilized to identify SARS-CoV 2 in various samples utilizing portable devices, as well as any potential applications for smartphones in epidemiological research and detection. The point of care (POC) employs a range of microfluidic biosensors based on smartphones, including molecular sensors, immunological biosensors, hybrid biosensors, and imaging biosensors. For example, a number of tools have been created for the diagnosis of COVID-19, based on various theories. Integrated portable devices can be created using loop-mediated isothermal amplification, which combines isothermal amplification methods with colorimetric detection. Electrochemical approaches have been regarded as a potential substitute for optical sensing techniques that utilize fluorescence for detection and as being more beneficial to the Minimizing and simplicity of the tools used for detection, together with techniques that can amplify DNA or RNA under constant temperature conditions, without the need for repeated heating and cooling cycles. Many research have used smartphones for virus detection and data visualization, making these techniques more user-friendly and broadly distributed throughout nations. Overall, our research provides a review of different novel, non-invasive, affordable, and efficient methods for identifying COVID-19 contagious infected people and halting the disease's transmission.

Spatially confining copper nanoclusters in porous ZrO2 for fluorescence/colorimetry/smartphone triple-mode detection of metoprolol tartrate

Sensitive detection of metoprolol tartrate (MPT) is extremely urgent in the therapy of cardiovascular diseases to guarantee the curative effectiveness. Herein, porous ZrO₂ was first employed as a matrix to spatially confine CuNCs (ZrO₂@CuNCs), which simultaneously ameliorated the emission intensity and stability of CuNCs. Benefiting from the inner filter effect (IFE) and dynamic quenching effect (DQE) between ZrO₂@CuNCs and AuNPs and the color fading of AuNPs induced by MPT, fluorometric and colorimetric methods for simple and sensitive determination of MPT were proposed. Besides, to meet the demand of convenient detection of MPT, a portable sensing platform was constructed including a dark box produced by a 3D printer and a smartphone. This method was further employed to determine MPT in human serum and urine samples with satisfactory results with the triple mode. This work is the first attempt to fabricate a multi-mode optical and portable sensor for MPT detection, which provides a novel approach for point-of-care monitoring of drugs in the treatment of diseases.