Improving diagnostic performance of coronavirus disease 2019 rapid antigen testing through computer-based feedback training using open-source experimental psychology software.

INTRODUCTION: Rapid antigen testing (RAT) results are visually read as whether colored line is present or absent. The subjective interpretation potentially misses detecting weak lines due to lower analyte concentration in samples tested, requiring training. Although routine test experience has improved the result readout skills, it consumes time and resources. Therefore, we created a computer-based feedback training method using open-source experimental psychology software, wherein participants accumulate RAT result readout experience by repeatedly responding positive/negative to randomly presented pictures showing RAT results; then, they receive feedback on their answers as correct or incorrect and are asked to stare at the pictures again with the knowledge of correct answer. This study aimed to examine the training effects in improving the skills, using coronavirus disease 2019 (COVID-19) RAT. METHODS: Twenty-two medical technologists were randomly divided into two groups: the feedback-training and test-experience groups. Using several pictures showing positive and negative results of COVID-19 RAT, after examination of their initial result readout skills, feedback-training group received the feedback training, whereas test-experience group performed an equal number of tests without feedback to accumulate test experience, and their skills were examined again. The ratio of "positive" answers to the pictures showing positive results (i.e., hit rate) was statistically analyzed. RESULTS: The feedback-training group showed a significantly higher hit rate after their training, whereas the test-experience group did not. The feedback training effects were manifested in weak line detection. CONCLUSIONS: This computer-based feedback training method can be an effective tool for improving RAT result readout skills.

Dual Functional Ultrasensitive Point-of-Care Clinical Diagnosis Using Metal-Organic Frameworks-Based Immunobeads.

Sepsis is an acute systemic infectious syndrome with high fatality. Fast and accurate diagnosis, monitoring, and medication of sepsis are essential. We exploited the fluorescent metal-AIEgen frameworks (MAFs) and demonstrated the dual functions of protein detection and bacteria identification: (i) ultrasensitive point-of-care (POC) detection of sepsis biomarkers (100 times enhanced sensitivity); (ii) rapid POC identification of Gram-negative/positive bacteria (selective aggregation within 20 min). Fluorescent lateral flow immunoassays (LFAs) are convenient and inexpensive for POC tests. MAFs possess a large surface area, excellent photostability, high quantum yield (∼80%), and multiple active sites serving as protein binding domains for ultrasensitive detection of sepsis biomarkers (IL-6/PCT) on LFAs. The limit of detection (LOD) for IL-6/PCT is 0.252/0.333 pg/mL. Rapid appraisal of infectious bacteria is vital to guide the use of medicines. The dual-functional fluorescent MAFs have great potential in POC tests for the clinical diagnosis of bacterial infections.

An Artificial Miniaturized Peroxidase for Signal Amplification in Lateral Flow Immunoassays.

Signal amplification strategies are widely used for improving the sensitivity of lateral flow immunoassays (LFiAs). Herein, the artificial miniaturized peroxidase Fe(III)-MimochromeVI*a (FeMC6*a), immobilized on gold nanoparticles (AuNPs), is used as a strategy to obtain catalytic signal amplification in sandwich immunoassays on lateral flow strips. The assay scheme uses AuNPs decorated with the mini-peroxidase FeMC6*a and anti-human-IgG as a detection antibody (dAb), for the detection of human-IgG, as a model analyte. Recognition of the analyte by the capture and detection antibodies is first evidenced by the appearance of a red color in the test line (TL), due to the accumulation of AuNPs. Subsequent addition of 3,3',5,5'-tetramethylbenzidine (TMB) induces an increase of the test line color, due to the TMB being converted into an insoluble colored product, catalyzed by FeMC6*a. This work shows that FeMC6*a acts as an efficient catalyst in paper, increasing the sensitivity of an LFiA up to four times with respect to a conventional LFiA. Furthermore, FeMC6*a achieves lower limits of detection that are found in control experiments where it is replaced with horseradish peroxidase (HRP), its natural counterpart. This study represents a significant proof-of-concept for the development of more sensitive LFiAs, for different analytes, based on properly designed artificial metalloenzymes.

Engineered Collaborative Size Regulation and Shape Engineering of Tremella-Like Au-MnOx for Highly Sensitive Bimodal-Type Lateral Flow Immunoassays.

Engineered collaborative size regulation and shape engineering of multi-functional nanomaterials (NPs) offer extraordinary opportunities for improving the analysis performance. It is anticipated to address the difficulty in distinguishing color changes caused by subtle variations in target concentrations, thereby facilitating the highly sensitive analysis of lateral flow immunoassays (LFIAs). Herein, tremella-like gold-manganese oxide (Au-MnOx ) nanoparticles with precise MnCl2 regulation are synthesized as immuno signal tracers via a facile one-step redox reaction in alkaline condition at ambient temperature. Avail of the tunable elemental composition and anisotropy in morphology, black-colored tremella-like Au-MnOx exhibits superb colorimetric signal brightness, enhanced antibody coupling efficiency, marvelous photothermal performance, and unrestricted immunological recognition affinity, all of which facilitate highly sensitive multi-signal transduction patterns. In conjunction with the handheld thermal reader device, a bimodal-type LFIA that combines size-regulation- and shape-engineering-mediated colorimetric-photothermal dual-response assay (coined as the SSCPD assay) with a limit of detection of 0.012 ng mL-1 for ractopamine (RAC) monitoring is achieved by integrating Au-MnOx with the competitive-type immunoreaction. This work illustrates the effectiveness of this strategy for establishing high-performance sensing, and the SSCPD assay may be extended to a wide spectrum of future point-of-care (POC) diagnostic applications.

An overview of the most important preanalytical factors influencing the clinical performance of SARS-CoV-2 antigen rapid diagnostic tests (Ag-RDTs).

Due to the many technical limitations of molecular biology, the possibility to sustain enormous volumes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) diagnostic testing relies strongly on the use of antigen rapid diagnostic tests (Ag-RDTs). Besides a limited analytical sensitivity, the manually intensive test procedures needed for performing these tests, very often performed by unskilled personnel or by the patients themselves, may contribute to considerably impair their diagnostic accuracy. We provide here an updated overview on the leading preanalytical drawbacks that may impair SARS-CoV-2 Ag-RDT accuracy, and which encompass lower diagnostic sensitivity in certain age groups, in asymptomatic subjects and those with a longer time from symptoms onset, in vaccine recipients, in individuals not appropriately trained to their usage, in those recently using oral or nasal virucidal agents, in oropharyngeal swabs and saliva, as well as in circumstances when instructions provided by the manufacturers are unclear, incomplete or scarcely readable and intelligible. Acknowledging these important preanalytical limitations will lead the way to a better, more clinically efficient and even safer use of this important technology, which represents an extremely valuable resource for management of the ongoing pandemic.

Assessment of two brands of fentanyl test strips with 251 synthetic opioids reveals "blind spots" in detection capabilities.

BACKGROUND: Fentanyl test strips (FTS) are a commonly deployed tool in drug checking, used to test for the presence of fentanyl in street drug samples prior to consumption. Previous reports indicate that in addition to fentanyl, FTS can also detect fentanyl analogs like acetyl fentanyl and butyryl fentanyl, with conflicting reports on their ability to detect fentanyl analogs like Carfentanil and furanyl fentanyl. Yet with hundreds of known fentanyl analogs, there has been no large-scale study rationalizing FTS reactivity to different fentanyl analogs. METHODS: In this study, 251 synthetic opioids-including 214 fentanyl analogs-were screened on two brands of fentanyl test strips to (1) assess the differences in the ability of two brands of fentanyl test strips to detect fentanyl-related compounds and (2) determine which moieties in fentanyl analog chemical structures are most crucial for FTS detection. Two FTS brands were assessed in this study: BTNX Rapid Response and WHPM DanceSafe. RESULTS: Of 251 screened compounds assessed, 121 compounds were detectable at or below 20,000 ng/mL by both BTNX and DanceSafe FTS, 50 were not detectable by either brand, and 80 were detectable by one brand but not the other (n = 52 BTNX, n = 28 DanceSafe). A structural analysis of fentanyl analogs screened revealed that in general, bulky modifications to the phenethyl moiety inhibit detection by BTNX FTS while bulky modifications to the carbonyl moiety inhibit detection by DanceSafe FTS. CONCLUSIONS: The different "blind spots" are caused by different haptens used to elicit the antibodies for these different strips. By utilizing both brands of FTS in routine drug checking, users could increase the chances of detecting fentanyl analogs in the "blind spot" of one brand.

New Perspective on Planar Inductive Sensors: Radio-Frequency Refractometry for Highly Sensitive Quantification of Magnetic Nanoparticles.

We demonstrate how resonant planar coils may be used as sensors to detect and quantify magnetic nanoparticles reliably. A coil's resonant frequency depends on the adjacent materials' magnetic permeability and electric permittivity. A small number of nanoparticles dispersed on a supporting matrix on top of a planar coil circuit may thus be quantified. Such nanoparticle detection has application detection to create new devices to assess biomedicine, food quality assurance, and environmental control challenges. We developed a mathematical model for the inductive sensor response at radio frequencies to obtain the nanoparticles' mass from the self-resonance frequency of the coil. In the model, the calibration parameters only depend on the refraction index of the material around the coil, not on the separate magnetic permeability and electric permittivity. The model compares favourably with three-dimensional electromagnetic simulations and independent experimental measurements. The sensor can be scaled and automated in portable devices to measure small quantities of nanoparticles at a low cost. The resonant sensor combined with the mathematical model is a significant improvement over simple inductive sensors, which operate at smaller frequencies and do not have the required sensitivity, and oscillator-based inductive sensors, which focus on just magnetic permeability.

Updates on the Biofunctionalization of Gold Nanoparticles for the Rapid and Sensitive Multiplatform Diagnosis of SARS-CoV-2 Virus and Its Proteins: From Computational Models to Validation in Human Samples.

Since the outbreak of the pandemic respiratory virus SARS-CoV-2 (COVID-19), academic communities and governments/private companies have used several detection techniques based on gold nanoparticles (AuNPs). In this emergency context, colloidal AuNPs are highly valuable easy-to-synthesize biocompatible materials that can be used for different functionalization strategies and rapid viral immunodiagnosis. In this review, the latest multidisciplinary developments in the bioconjugation of AuNPs for the detection of SARS-CoV-2 virus and its proteins in (spiked) real samples are discussed for the first time, with reference to the optimal parameters provided by three approaches: one theoretical, via computational prediction, and two experimental, using dry and wet chemistry based on single/multistep protocols. Overall, to achieve high specificity and low detection limits for the target viral biomolecules, optimal running buffers for bioreagent dilutions and nanostructure washes should be validated before conducting optical, electrochemical, and acoustic biosensing investigations. Indeed, there is plenty of room for improvement in using gold nanomaterials as stable platforms for ultrasensitive and simultaneous "in vitro" detection by the untrained public of the whole SARS-CoV-2 virus, its proteins, and specific developed IgA/IgM/IgG antibodies (Ab) in bodily fluids. Hence, the lateral flow assay (LFA) approach is a quick and judicious solution to combating the pandemic. In this context, the author classifies LFAs according to four generations to guide readers in the future development of multifunctional biosensing platforms. Undoubtedly, the LFA kit market will continue to improve, adapting researchers' multidetection platforms for smartphones with easy-to-analyze results, and establishing user-friendly tools for more effective preventive and medical treatments.

Engineered Core-Shell Multifunctional Nano-Tracer in Raman-Silent Region with Highly Retained Affinity to Enhance Lateral Flow Immunoassays.

Stimulated surface-enhanced Raman scattering (SERS) in combination with engineered nano-tracer offers extraordinary potential in lateral flow immunoassays (LFIAs). Nonetheless, the investigation execution of SERS-LFIA is often compromised by the intricacy and overlap of the Raman fingerprint spectrum as well as the affinity-interference of nano-tracer to antibody. To circumvent these critical issues, an engineered core-shell multifunctional nano-tracer (named APNPs) with precise control of the size of nano-core (AuNPs) and coating of the nano-shell (Prussian blue nanomaterials) is prepared for SERS-LFIA via a modified enlarging particle size and coating modification strategy. Importantly, this nano-tracer exhibits enhanced coupling efficiency, highly retained affinity, reinforced colloid stability, and unique SERS signal (2156 cm-1 ) in the silent region (1800-2800 cm-1 ) with high signal-to-background ratio simultaneously, all of which are beneficial to the enhancement of the analysis performance. With a proof-of-concept demonstration for detection of ractopamine (RAC), a dual-pattern LFIA that synergizes both the enlarged particle size and coating modification supported colorimetric/biological silence Raman dual-response (coined as the ECCRD assay) is demonstrated by integrating APNPs with the competitive-type immunoreaction. This research may contribute to the rational design of multifunctional nano-tracer, and the ECCRD assay can be expanded for a wide spectrum of applications in environmental monitoring and biomedical diagnosis.

Highly sensitive protein detection using recombinant spores and lateral flow immunoassay.

Lateral flow immunoassays (LFIs) can be used to detect intact bacteria or spores; when gold nanoparticles (AuNPs) are used as the signal reporters, the detection limits are very low. Spore-based surface display has been widely studied for enzyme immobilization and live-nontoxic oral vaccines. In this study, recombinant spores were used to improve the sensitivity of a LFI. We developed a test kit that combines streptavidin-displayed spores with a LFI assay for rapid protein detection. The recombinant spores served as a signal amplifier and AuNPs were used as the signal reporters. For detection of ß-galactosidase, which was used as the model protein, the detection limit was about 10-15 mol, while that of the conventional LFI is about 10-12 mol. In both methods, nanogold was used as the colorimetric signal and could be observed with the naked eye. This method improved LFI sensitivity without sacrificing its advantages. Furthermore, enhanced green fluorescent protein (eGFP) was also displayed on the surface of the streptavidin-displayed spores. Without AuNPs, the fluorescent recombinant spores acted as the signal, which could be detected by a fluorescence detector, such as a fluorescence microscope. The detection limit was 10-16 mol under fluorescence microscopy whose magnification was 25-fold. Therefore, in conclusion, in this proof of concept study, the detection limits of both proposed methods were far superior to those of traditional LFI assay.

Antibody- and nucleic acid-based lateral flow immunoassay for Listeria monocytogenes detection.

Listeria monocytogenes is an invasive opportunistic foodborne pathogen and its routine surveillance is critical for protecting the food supply and public health. The traditional detection methods are time-consuming and require trained personnel. Lateral flow immunoassay (LFIA), on the other hand, is an easy-to-perform, rapid point-of-care test and has been widely used as an inexpensive surveillance tool. In recent times, nucleic acid-based lateral flow immunoassays (NALFIA) are also developed to improve sensitivity and specificity. A significant improvement in lateral flow-based assays has been reported in recent years, especially the ligands (antibodies, nucleic acids, aptamers, bacteriophage), labeling molecules, and overall assay configurations to improve detection sensitivity, specificity, and automated interpretation of results. In most commercial applications, LFIA has been used with enriched food/environmental samples to ensure detection of live cells thus prolonging the assay time to 24-48 h; however, with the recent improvement in LFIA sensitivity, results can be obtained in less than 8 h with shortened and improved enrichment practices. Incorporation of surface-enhanced Raman spectroscopy and/or immunomagnetic separation could significantly improve LFIA sensitivity for near-real-time point-of-care detection of L. monocytogenes for food safety and public health applications.

Ru(bpy)32+ -Loaded Mesoporous Silica Nanoparticles as Electrochemiluminescent Probes of a Lateral Flow Immunosensor for Highly Sensitive and Quantitative Detection of Troponin I.

The lateral flow immunosensor (LFI) is a widely used diagnostic tool for biomarker detection; however, its sensitivity is often insufficient for analyzing targets at low concentrations. Here, an electrochemiluminescent LFI (ECL-LFI) is developed for highly sensitive detection of troponin I (TnI) using Ru(bpy)32+ -loaded mesoporous silica nanoparticles (RMSNs). A large amount of Ru(bpy)32+ is successfully loaded into the mesoporous silica nanoparticles with excellent loading capacity and shows strong ECL signals in reaction to tripropylamine. Antibody-immobilized RMSNs are applied to detect TnI by fluorescence and ECL analysis after a sandwich immunoassay on the ECL-LFI strip. The ECL-LFI enables the highly sensitive detection of TnI-spiked human serum within 20 min at femtomolar levels (≈0.81 pg mL-1 ) and with a wide dynamic range (0.001-100 ng mL-1 ), significantly outperforming conventional fluorescence detection (>3 orders of magnitude). Furthermore, TnI concentrations in 35 clinical serum samples across a low range (0.01-48.31 ng mL-1 ) are successfully quantified with an excellent linear correlation (R2  = 0.9915) using a clinical immunoassay analyzer. These results demonstrate the efficacy of this system as a high-performance sensing strategy capable of capitalizing on future point-of-care testing markets for biomolecule detection.

Evaluation of three immunochromatographic tests for rapid detection of antibodies against SARS-CoV-2.

Lateral flow immunoassays (LFIA) for rapid detection of specific antibodies (IgM and IgG) against SARS-CoV-2 in different human specimens have been developed in response to the pandemic. The aim of this study is to evaluate three immunocromathographic assays (Sienna®, Wondfo® and Prometheus®) for detection of antibodies against SARS-CoV-2 in serum samples, considering RT-qPCR as a reference. A total of 145 serum samples from 145 patients with clinical suspicion of COVID-19 were collected: all of the samples were tested with Sienna®, 117 with Wondfo® and 89 with Prometheus®. The overall results of sensitivity, specificity, positive predictive value and negative predictive value obtained were as follows: 64.4%, 75%, 85.5% and 47.8% with Sienna®; 45.2%, 81.8%, 80.5% and 47.4% with Wondfo® and 75.5%, 12.5%, 51.4% and 29.4% with Prometheus®. The accuracy of the test for Sienna®, Wondfo® and Prometheus® was 67.6%, 59% and 47.2%, with a prevalence of COVID-19 of 69.7%, 62.4% and 55.1% respectively. Sensitivity of the three tests (Sienna®, Wondfo® and Prometheus® respectively) along the three different stages was 36.6%, 18.8% and 68.6% in the early stage (first week); 81.3%, 74.1% and 90.9% in the intermediate stage (second week) and 100%, 83.3% and 100% in the late stage (third week). The results demonstrate that even though Prometheus® presented a high sensitivity, the specificity was notably lower than the other two tests. Sienna® showed the greatest contrast between sensitivity and specificity, achieving the best accuracy, followed by Wondfo®. The sensitivity of the three ICT assays was higher in late stages of the disease.

Integrated gold superparticles into lateral flow immunoassays for the rapid and sensitive detection of Escherichia coli O157:H7 in milk.

Escherichia coli O157:H7 is a common harmful foodborne pathogen that can cause severe diseases at low infectious doses. Traditional lateral flow immunoassay (LFIA) for the rapid screening of E. coli O157:H7 in food suffers from low sensitivity due to its dependence on 20- to 40-nm gold nanoparticles (AuNP) with insufficient brightness as labels. To address this issue, we reported for the first time the successful synthesis of gold superparticles (GSP) by encapsulating numerous small AuNP into a polymer nanobead using an evaporation-induced self-assembly method. Results indicated that the resultant GSP exhibited remarkably enhanced absorbance compared with the most widely used 40 nm AuNP in LFIA. In addition, the absorbance of GSP could be easily tuned by varying GSP sizes. Under optimized conditions, we achieved a rapid and sensitive determination of E. coli O157:H7 in milk with a detection limit of 5.95 × 102 cfu/mL when using the GSP with a size of 342 nm as LFIA signal reporters, exhibiting improvement of approximately 32-fold relative to the conventional 40 nm AuNP-LFIA method. We further demonstrated the selectivity, accuracy, reliability, and practicality of the proposed GSP-LFIA strip. In summary, this work offers a new strategy for improving LFIA sensitivity using assembled GSP as markers and demonstrates huge potential in rapidly and sensitively detecting foodborne pathogens.

Simplified formats of modern biosensors: 60 years of using immunochromatographic test systems in laboratory diagnostics.

Immunochromatographic test systems known to foreign laboratory diagnostic experts as lateral flow immunoassay (LFIA) are simplified tape formats of modern biosensors. For 60 years, they have been widely used for the rapid detection of target molecules (ligands) in biosubstrates and the diagnosis of many diseases and conditions. The growing popularity of these test systems for providing medical care or diagnostics in developing countries, medical facilities, in emergency situations, as well as for individual home use by patients while monitoring their health are the main factors contributing to the continuous development and improvement of these methods, the emergence of a new generation of formats. The attractiveness and popularity of these fast, easy-to-use, inexpensive and portable diagnostic tools is associated primarily with their high analytical sensitivity and specificity, as well as the ease of interpretation of the results. These qualities have passed the test of time, and today LFIA test systems are fully consistent with the modern world concept of «point-of-care testing¼, finding wide application not only in medicine, but also in ecology, veterinary medicine, and agriculture. This review will highlight the modern principles of designing the most widely used formats of immunochromatographic test systems for clinical laboratory diagnostics, summarize the main advantages and disadvantages of the method, as well as current achievements and prospects of LFIA technology. Modern innovations aimed at improving the analytical characteristics of LFIA technology are interesting, promising and can bring additional benefits to immunochromatographic platforms that have gained popularity and attractiveness for six decades.

Quantifying the effect of swab pool size on the detection of influenza A viruses in broiler chickens and its implications for surveillance.

BACKGROUND: Timely diagnosis of influenza A virus infections is critical for outbreak control. Due to their rapidity and other logistical advantages, lateral flow immunoassays can support influenza A virus surveillance programs and here, their field performance was proactively assessed. The performance of real-time polymerase chain reaction and two lateral flow immunoassay kits (FluDETECT and VetScan) in detecting low pathogenicity influenza A virus in oropharyngeal swab samples from experimentally inoculated broiler chickens was evaluated and at a flock-level, different testing scenarios were analyzed. RESULTS: For real-time polymerase chain reaction positive individual-swabs, FluDETECT respectively detected 37% and 58% for the H5 and H7 LPAIV compared to 28% and 42% for VetScan. The mean virus titer in H7 samples was higher than for H5 samples. For real-time polymerase chain reaction positive pooled swabs (containing one positive), detections by FluDETECT were significantly higher in the combined 5- and 6-swab samples compared to 11-swab samples. FluDETECT detected 58%, 55.1% and 44.9% for the H7 subtype and 28.3%, 34.0% and 24.6% for the H5 in pools of 5, 6 and 11 respectively. In our testing scenario analysis, at low flock-level LPAIV infection prevalence, testing pools of 11 detected slightly more infections while at higher prevalence, testing pools of 5 or 6 performed better. For highly pathogenic avian influenza virus, testing pools of 11 (versus 5 or 6) detected up to 5% more infections under the assumption of similar sensitivity across pools and detected less by 3% when its sensitivity was assumed to be lower. CONCLUSIONS: Much as pooling a bigger number of swab samples increases the chances of having a positive swab included in the sample to be tested, this study's outcomes indicate that this practice may actually reduce the chances of detecting the virus since it may result into lowering the virus titer of the pooled sample. Further analysis on whether having more than one positive swab in a pooled sample would result in increased sensitivity for low pathogenicity avian influenza virus is needed.

Significant Sensitivity Improvement for Camera-Based Lateral Flow Immunoassay Readers.

Recent developments in smartphone-based strip readers have further improved the performances of lateral flow test kits. Most smartphone cameras encode an unaltered and nonlinear power-law transfer function that maps the light intensity to a pixel value; this poses some limitations for camera-based strip readers. For faint-color test lines which are almost as white such as with nitrocellulose pads, the slope of the transfer function is low. Therefore, it is difficult to differentiate between the faint test lines and the white background. We show that by manually setting the camera exposure time-instead of using the automatic settings-to the high-slope region of the transfer function, the reader's sensitivity can be improved. We found that the sensitivity and the limit of detection of the Acidovorax avenae subsp. citrulli (Aac) test kit were enhanced up to 3-fold and 5-fold, respectively, when using the readers at the optimal camera settings, compared to the automatic mode settings. This simple technique can be readily applied to any existing camera-based colorimetric strip reader to significantly improve its performance.

Opportunities and challenges for the application of microfluidic technologies in point-of-care veterinary diagnostics.

There is a growing need for low-cost, rapid and reliable diagnostic results in veterinary medicine. Point-of-care (POC) tests have tremendous advantages over existing laboratory-based tests, due to their intrinsic low-cost and rapidity. A considerable number of POC tests are presently available, mostly in dipstick or lateral flow formats, allowing cost-effective and decentralised diagnosis of a wide range of infectious diseases and public health related threats. Although, extremely useful, these tests come with some limitations. Recent advances in the field of microfluidics have brought about new and exciting opportunities for human health diagnostics, and there is now great potential for these new technologies to be applied in the field of veterinary diagnostics. This review appraises currently available POC tests in veterinary medicine, taking into consideration their usefulness and limitations, whilst exploring possible applications for new and emerging technologies, in order to widen and improve the range of POC tests available.

Significance of the antibody orientation for the lateral flow immunoassays: A mini-review.

Lateral flow immunoassays (LFIAs) are well-established and broadly commercialized tools in the field of point-of-care testing due to their simplicity, rapidity, cost-effectiveness, and low requirements for users and equipment. However, the insensitivity and the possibility of producing inaccurate results associated with conventional LFIAs have impeded their wide-ranging implementation, especially for monitoring ultra-trace level of analytes. Moreover, the heterogeneous distribution of amino acids on the surface of antibody (Ab) results in a lack of precise control over their orientation, which ultimately leads to unsatisfactory detection performance. To address those concerns, herein we provide an overview of the emerging efforts to prepare well-established LFIAs from the perspective of orientation manipulation of immobilized Abs on the nanoprobes or membranes. The preparation of excellent nanoprobes with Abs being oriented immobilized, consisting of the nanoprobe types, Ab types, and their conjugation chemistries, are reviewed. Followed by the introduction of efforts highlight the importance of directionally immobilized Ab on the membrane. The effects of Ab orientation on the analytical performance of LFIA platforms in terms of sensitivity, specificity, rapidity, reliability, cost-effectiveness, and stability are also summarized. Finally, the future development and challenges of Ab-oriented immobilization-assisted LFIAs are also discussed.

Polydopamine modified colloidal gold nanotag-based lateral flow immunoassay platform for highly sensitive detection of pathogenic bacteria and fast evaluation of antibacterial agents.

Bacterial infection is a great threat to human health. Lateral flow immunoassays (LFIAs) with the merits of low cost, quick screening, and on-site detection are competitive technologies for bacteria detection, but their detection limits depend on the optical performance of the adopted nanotags. Herein, we presented a LFIA platform for bacteria detection using polydopamine (PDA) functionalized Au nanoparticles (denoted as Au@PDA) as the nanotag. The introduction of PDA could provide enhanced light absorption of Au, as well as numerous functional groups for conjugation. Small recognition molecules i.e. vancomycin (Van) and p-mercaptophenylboronic acid (PMBA) were covalently anchored to Au@PDA, and selected as the specific probes towards Gram-positive (G+) and Gram-negative (G-) bacteria, respectively. Taken Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) as the representative targets of G+ and G- bacteria, two LFA strips were successfully constructed based on the immuno-sandwich principle. They could quantitatively detect S. aureus and E. coli both down to 102 cfu/mL, a very competitive detection limit in comparison with other colorimetric or luminescent probes-based LFIAs. Furthermore, the proposed two strips were applied for the quantitative, accurate, and rapid detection of S. aureus and E. coli in food and human urine samples with good analytical results obtained. In addition, they were integrated as a screening platform for quick evaluation of diverse antibacterial agents within 3 h, which is remarkably shortened compared with that of the two traditional methods i.e. bacterial culture and plate-counting.