Rapid and quantitative detection of prostate specific antigen with a quantum dot nanobeads-based immunochromatography test strip

Broad-spectrum antibody against thiazides and degraded salamide and immunoassay establishment for simultaneous detection

The illegal additive thiazides and degraded salamide in food supplements poses significant health risks and regulatory challenges. However, the structural differences between thiazides and salamide complicate the hapten design for immunoassay detection. In this study, we first outlined the common skeleton of thiazides and their shared epitopes with salamide through molecular overlap and atomic charge distribution analysis. Several haptens were rationally designed based on the private epitope of salamide and the shared epitopes with thiazides, assisted by computer-aided chemical analysis. Subsequently, the resultant monoclonal antibody exhibited broad specificity for thiazides (IC50 value = 21.43-405.40 ng/mL) and salamide (IC50 value = 0.76 ng/mL). The immunoassay affinities of 5 of these thiazides are reported for the first time. Further elucidation of the intrinsic recognition mechanism was achieved through homology modeling and molecular docking, clarifying the antibody's diverse recognition spectrum. Finally, we established a rapid, reliable colloidal gold-based immunochromatography strip for simultaneous detecting total thiazides and degraded salamide in food supplements and surface water sample for the first time. The cut-off value was as low as 7.5 ng/mL, which was 32 times more sensitive than that of established immunoassays for thiazides.

A high sensitivity prostate-specific antigen SERS detection platform based on laser resonance nanoparticles

Accurate quantitative analysis of cancer-related specific biomarkers in clinical serum is very important for the early diagnosis and treatment of cancer. Hospitals often use serum prostate-specific antigen (PSA) as a biomarker associated with prostate cancer diagnosis and prognosis, and prostate cancer cells often produce more PSA than benign cells, leading to elevated PSA levels in the blood. In this study, an immunoassay based on surface-enhanced Raman scattering (SERS) was established for the detection of PSA employing magnetic beads along with SERS nanotags. The hospital currently takes two hours to test the results, the equipment price is high, and the detection price is high, and the penetration rate in township hospitals in China is low. SERS has super-sensitive and fast detection ability, and the availability of the detection result in 10 minutes significantly reduces the waiting time. Besides, the detection method is simple, cheap and portable, making it suitable for township health centers. To evaluate the clinical applicability of this method, 75 male clinical serum samples were tested, most of which were in the gray area of 4.0-10.0 ng mL-1. The experimental results show that our detection method has good agreement with the results measured by the electrochemical luminescence (ECL) system in the hospital clinical laboratory. Our detection limit for actual samples from patients can reach 0.029 ng mL-1. Therefore, our clinical serum PSA marker detection method based on SERS has a great potential market in towns and villages.

A Portable Fluorescent Lateral Flow Immunoassay Platform for Rapid Detection of FluA

The spread of the FluA virus poses significant public health concerns worldwide. Fluorescent lateral flow immunoassay (LFIA) test strips have emerged as vital tools for the early detection and monitoring of influenza infections. However, existing quantitative virus-detection methods, particularly those utilizing smartphone-based sensing platforms, encounter accessibility challenges in resource-limited areas and among the elderly population. Despite their advantages in speed and portability, these platforms often lack user-friendliness for these demographics, impeding their widespread utilization. To address these challenges, this study proposes leveraging the optical pick-up unit (OPU) sourced from commercial optical drives as a readily available fluorescence excitation module for the quantitative detection of antibodies labeled with quantum-dot fluorescent microspheres. Additionally, we utilize miniaturized and high-performance optical components and 3D-printed parts, along with a customized control system, to develop an affordable point-of-care testing (POCT) device. Within the system, a stepping motor scans the test strip from the T-line to the C-line, enabling the calculation of the fluorescence-intensity ratio between the two lines. This simple yet effective design facilitates rapid and straightforward field or at-home testing for FluA. The proposed prototype platform demonstrates promising performance, achieving a limit of detection (LOD) of 2.91 ng/mL, a total detection time of no more than 15 min, and dimensions of 151 mm × 11.2 mm × 10.8 mm3. We believe that the proposed approach holds great potential for improving access to an accurate influenza diagnosis.

A Comprehensive Review and Androgen Deprivation Therapy and Its Impact on Alzheimer's Disease Risk in Older Men with Prostate Cancer

Prostate cancer (PCa) is one of the most prevalent malignancies affecting males worldwide. Despite reductions in mortality rates due to advances in early identification and treatment methods, PCa remains a major health concern. Recent research has shed light on a possible link between PCa and Alzheimer's disease (AD), which is a significant neurological ailment that affects older males all over the world. Androgen deprivation therapy (ADT), a cornerstone therapeutic method used in conjunction with radiation and palliative care in advanced metastatic PCa cases, is critical for disease management. Evidence reveals a relationship between ADT and cognitive impairment. Hormonal manipulation may cause long-term cognitive problems through processes such as amyloid beta (Aβ) aggregation and neurofibrillary tangles (NFTs). Fluctuations in basal androgen levels can upset the delicate balance of genes that are sensitive to androgen levels, contributing to cognitive impairment. This detailed review dives into the various aspects of PCa aetiology and its relationship with cognitive decline. It investigates the discovery of particular biomarkers, as well as microRNAs (miRNAs), which play important roles in pathogenic progression. The review attempts to identify potential biomarkers associated with ADT-induced cerebral changes, including Aβ oligomer buildup, NFT formation, and tauopathy, which can contribute to early-onset dementia and cognitive impairment. Besides it further aims to provide insights into innovative diagnostic and therapeutic avenues for alleviating PCa and ADT-related cognitive sequelae by unravelling these complicated pathways and molecular mechanisms.

Research progress on preparation methods and sensing applications of molecularly imprinted polymer-aptamer dual recognition elements

The aptamer (Apt) and the molecularly imprinted polymer (MIP), as effective substitutes for antibodies, have received widespread attention from researchers because of their creation. However, the low stability of Apt in harsh detection environment and the poor specificity of MIP have hindered their development. Therefore, some researchers have attempted to combine MIP with Apt to explore whether the effect of "1 + 1 > 2" can be achieved. Since its first report in 2013, MIP-Apt dual recognition elements have become a highly focused research direction in the fields of biology and chemistry. MIP-Apt dual recognition elements not only possess the high specificity of Apt and the high stability of MIP in harsh detection environment, but also have high sensitivity and affinity. They have been successfully applied in medical diagnosis, food safety, and environmental monitoring fields. This article provides a systematic overview of three preparation methods for MIP-Apt dual recognition elements and their application in eight different types of sensors. It also provides effective insights into the problems and development directions faced by MIP-Apt dual recognition elements.

Point-of-Care Prostate Specific Antigen Testing: Examining Translational Progress toward Clinical Implementation

Prostate cancer (PCa) is the second most common male cancer and is attributable to over 375,000 deaths annually. Prostate specific antigen (PSA) is a key biomarker for PCa and therefore measuring patient PSA levels is an important aspect of the diagnostic pathway. Automated immunoassays are currently utilized for PSA analysis, but they require a laboratory setting with specialized equipment and trained personnel. This results in high diagnostic costs, extended therapeutic turnaround times, and restrictions on testing capabilities in resource-limited settings. Consequently, there is a strong drive to develop point-of-care (PoC) PSA tests that can offer accurate, low-cost, and rapid results at the time and place of the patient. However, many emerging PoC tests experience a trade-off between accuracy, affordability, and accessibility which distinctly limits their translational potential. This review comprehensively assesses the translational advantages and limitations of emerging laboratory-level and commercial PoC tests for PSA determination. Electrochemical and optical PSA sensors from 2013 to 2023 are systematically examined. Furthermore, we suggest how the translational potential of emerging tests can be optimized to achieve clinical implementation and thus improve PCa diagnosis globally.

Lateral Flow Assay for Hepatitis B Detection: A Review of Current and New Assays

From acute to chronic hepatitis, cirrhosis, and hepatocellular cancer, hepatitis B infection causes a broad spectrum of liver diseases. Molecular and serological tests have been used to diagnose hepatitis B-related illnesses. Due to technology limitations, it is challenging to identify hepatitis B infection cases at an early stage, particularly in a low- and middle-income country with constrained resources. Generally, the gold-standard methods to detect hepatitis B virus (HBV) infection requires dedicated personnel, bulky, expensive equipment and reagents, and long processing times which delay the diagnosis of HBV. Thus, lateral flow assay (LFA), which is inexpensive, straightforward, portable, and operates reliably, has dominated point-of-care diagnostics. LFA consists of four parts: a sample pad where samples are dropped; a conjugate pad where labeled tags and biomarker components are combined; a nitrocellulose membrane with test and control lines for target DNA-probe DNA hybridization or antigen-antibody interaction; and a wicking pad where waste is stored. By modifying the pre-treatment during the sample preparation process or enhancing the signal of the biomarker probes on the membrane pad, the accuracy of the LFA for qualitative and quantitative analysis can be improved. In this review, we assembled the most recent developments in LFA technologies for the progress of hepatitis B infection detection. Prospects for ongoing development in this area are also covered.

The application of nanoparticles in point-of-care testing (POCT) immunoassays

The Covid-19 pandemic has led to greater recognition of the importance of the fast and timely detection of pathogens. Recent advances in point-of-care testing (POCT) technology have shown promising results for rapid diagnosis. Immunoassays are among the most extensive POCT assays, in which specific labels are used to indicate and amplify the immune signal. Nanoparticles (NPs) are above the rest because of their versatile properties. Much work has been devoted to NPs to find more efficient immunoassays. Herein, we comprehensively describe NP-based immunoassays with a focus on particle species and their specific applications. This review describes immunoassays along with key concepts surrounding their preparation and bioconjugation to show their defining role in immunosensors. The specific mechanisms, microfluidic immunoassays, electrochemical immunoassays (ELCAs), immunochromatographic assays (ICAs), enzyme-linked immunosorbent assays (ELISA), and microarrays are covered herein. For each mechanism, a working explanation of the appropriate background theory and formalism is articulated before examining the biosensing and related point-of-care (POC) utility. Given their maturity, some specific applications using different nanomaterials are discussed in more detail. Finally, we outline future challenges and perspectives to give a brief guideline for the development of appropriate platforms.

Portable Plasmonic Paper-Based Biosensor for Simple and Rapid Indirect Detection of CEACAM5 Biomarker via Metal-Enhanced Fluorescence

Rapid, simple, and sensitive analysis of relevant proteins is crucial in many research areas, such as clinical diagnosis and biomarker detection. In particular, clinical data on cancer biomarkers show great promise in forming reliable predictions for early cancer diagnostics, although the current analytical systems are difficult to implement in regions of limited recourses. Paper-based biosensors, in particular, have recently received great interest because they meet the criteria for point-of-care (PoC) devices; the main drawbacks with these devices are the low sensitivity and efficiency in performing quantitative measurements. In this work, we design a low-cost paper-based nanosensor through plasmonic calligraphy by directly drawing individual plasmonic lines on filter paper using a ballpoint pen filled with gold nanorods (AuNR) as the colloidal ink. The plasmonic arrays were further successively coated with negatively and positively charged polyelectrolyte layers employed as dielectric spacers to promote the enhancement of the emission of carboxyl-functionalized quantum dots (QD)—previously conjugated with specific antibodies—for indirect detection of the carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5). The efficiency, sensitivity, as well as the specificity of our portable nanosensor were validated by recording the luminescence of the QD@Ab complex when different concentrations of CEACAM5 were added dropwise onto the calligraphed plasmonic arrays.

Biosensors for detection of prostate cancer: a review

Diagnosis of prostate cancer (PC) has posed a challenge worldwide due to the sophisticated and costly diagnostics tools, which include DRE, TRUS, GSU, PET/CT scan, MRI, and biopsy. These diagnostic techniques are very helpful in the detection of PCs; however, all the techniques have their serious limitations. Biosensors are easier to fabricate and do not require any cutting-edge technology as required for other imaging techniques. In this regard, point-of-care (POC) biosensors are important due to their portability, convenience, low cost, and fast procedure. This review explains the various existing diagnostic tools for the detection of PCs and the limitation of these methods. It also focuses on the recent studies on biosensors technologies as an alternative to the conventional diagnostic techniques for the detection of PCs.

Mechanical Timer-Actuated Fluidic Dispensing System: Applications to an Automated Multistep Lateral Flow Immunoassay with High Sensitivity

In this study, we present a fluidic dispensing system that can automate the sequential fluidic delivery of multiple reagents for lateral flow assays. Highly sensitive assays typically require multiple solution-based sequences, including washing steps and signal amplification. However, implementation of these types of sequences on an automated and highly sensitive point-of-care testing (POCT) platform remains challenging. Our platform consists of two disposable cartridges with reagent chambers and a test strip and an instrument that has a mechanical timer to actuate the cam-follower-gear components. The timer rotation sequentially shifts the position of the chambers and loads the reagents to the test paper strip. The dispensing intervals are controlled at a variation of <1% within a total actuation time of 60 min. Unlike other POCT devices, the timing of fluid delivery in our timer-actuated platform is not dependent on the selection of substrates and reagents, and the unique approach to fluidic delivery results in no reagent overlap or carryover, minimal reagent loss, and highly accurate fluidic timing control for highly sensitive solution-based assays. As a model application, the proposed platform applies a gold enhancement solution to amplify the detection signal and detect prostate-specific antigen with a limit of detection of 86 pg/mL within 27 min. This platform provides an opportunity for solution-based POCT applications with high sensitivity, thereby satisfying the requirement for user-friendly operations in resource-limited settings.

Highly sensitive pregnancy test kit via oriented antibody conjugation on brush-type ligand-coated quantum beads

Lateral flow assays (LFA) enable development of portable and rapid diagnostic kits; however, their capacity to detect low levels of disease markers remains poor. Here, we report a highly sensitive pregnancy test kit as a proof of concept, by combining brush-type ligand-coated quantum beads (B-type QBs) and nanobody, which can control the antibody orientation and enhance sensitivity. The brush-type ligand provided excellent dispersion stability and high-binding capacity toward antibody. Fc-binding nanobody increased the antigen-binding capacity of conjugated antibodies on the B-type QBs. To facilitate convenient acquisition of the LFA results, we developed a smartphone-based reader with a 3D-printed optical imaging module, and validated the diagnostic performance of the sensing platform. The pregnancy test kit achieved a 5.1 pg mL^-1 limit of detection, corresponding to the levels for early-stage detection of heart disease and malaria. Our LFA application can potentially be expanded to diagnosis other diseases by simply changing the antibody pair in the kit.

Advances in quantum dots as diagnostic tools

Quantum dots (QDs) are crystalline inorganic semiconductor nanoparticles a few nanometers in size that possess unique optical electronic properties vs those of larger materials. For example, QDs usually exhibit a strong and long-lived photoluminescence emission, a feature dependent on size, shape and composition. These special optoelectronic properties make them a promising alternative to conventional luminescent dyes as optical labels in biomedical applications including biomarker quantification, biomolecule targeting and molecular imaging. A key parameter for use of QDs is to functionalize their surface with suitable (bio)molecules to provide stability in aqueous solutions and efficient and selective tagging biomolecules of interest. Researchers have successfully developed biocompatible QDs and have linked them to various biomolecule recognition elements, i.e., antibodies, proteins, DNA, etc. In this chapter, QD synthesis and characterization strategies are reviewed as well as the development of nanoplatforms for luminescent biosensing and imaging-guided targeting. Relevant biomedical applications are highlighted with a particular focus on recent progress in ultrasensitive detection of clinical biomarkers. Finally, key future research goals to functionalize QDs as diagnostic tools are explored.

Highly portable quantitative screening test for prostate-specific antigen at point of care

Prostate cancer (PCa) is the second most diagnosed cancer among men. Targeted PCa screening may decrease PCa-specific mortality. Prostate-specific antigen (PSA) is the most reliable and widely accepted tumor biomarker for screening and monitoring PCa status. However, in many settings, quantification of serum PSA requires access to centralized laboratories. In this study, we describe a proof-of-concept rapid test combined with a highly portable Cube^™ reader for quantification of total PSA from a drop of serum within 20 min. We demonstrated the application of gold nanoshells as a label for lateral flow assay with significant increase in the measured colorimetric signal intensity to achieve five times lower detection limit when compared to the traditionally used 40 nm gold nanosphere labels, without a need for any additional signal amplification steps. We first optimized and evaluated the performance of the assay with commercially available total PSA calibrators. For initial validation with commercially available ACCESS Hybritech PSA calibrator, a detection range of 0.5-150 ng/mL was achieved. We compared the performance of our total PSA test with IMMULITE analyzer for quantification of total PSA in archived human serum samples. On preliminary testing with archived serums samples and comparison with IMMULITE total PSA assay, a correlation of 0.95 (p < .0001) was observed. The highly portable quantitative screening test for PSA described in this study has the potential to make PCa screening more accessible where diagnostic labs and automated immunoassay systems are not available, to reduce therapeutic turnaround time, to streamline clinical care, and to direct patient care for both initial screening and for post-treatment monitoring of patients.

Photoluminescent Molecules and Materials as Diagnostic Reporters in Lateral Flow Assays

The lateral flow assay (LFA) is a point-of-care diagnostic test commonly available in an over-the-counter format because of its simplicity, speed, low cost, and portability. The reporter particles in these assays are among their most significant components because they perform the diagnostic readout and dictate the test's sensitivity. Today, gold nanoparticles are frequently used as reporters, but recent work focusing on photoluminescent-based reporter technologies has pushed LFAs to better performance. These efforts have focused specifically on reporters made of organic fluorophores, quantum dots, lanthanide chelates, persistent luminescent phosphors, and upconversion phosphors. In most cases, photoluminescent reporters show enhanced sensitivity compared to conventional gold nanoparticle-based assays. Here, we examine the advantages and disadvantages of these different reporters and highlight their potential benefits in LFAs. Our assessment shows that photoluminescent-based LFAs can not only reach lower detection limits than LFAs with traditional reporters, but they also can be capable of quantitative and multiplex analyte detection. As a result, the photoluminescent reporters make LFAs well-suited for medical diagnostics, the food and agricultural industry, and environmental testing.

Recent advances in nanomaterials for prostate cancer detection and diagnosis

Despite the significant progress in the discovery of biomarkers and the exploitation of technologies for prostate cancer (PCa) detection and diagnosis, the initial screening of these PCa-related biomarkers using current...

Sensitive and rapid determination of heat shock protein 70 using lateral flow immunostrips and upconversion nanoparticle fluorescence probes

Heat shock protein 70 (Hsp70), belonging to the heat shock protein (HSP) family, is reported to be a potential diagnostic biomarker.

Lateral Flow Immunoassay with Quantum-Dot-Embedded Silica Nanoparticles for Prostate-Specific Antigen Detection

Prostate cancer can be detected early by testing the presence of prostate-specific antigen (PSA) in the blood. Lateral flow immunoassay (LFIA) has been used because it is cost effective and easy to use and also has a rapid sample-to-answer process. Quantum dots (QDs) with very bright fluorescence have been previously used to improve the detection sensitivity of LFIAs. In the current study, a highly sensitive LFIA kit was devised using QD-embedded silica nanoparticles. In the present study, only a smartphone and a computer software program, ImageJ, were used, because the developed system had high sensitivity by using very bright nanoprobes. The limit of PSA detection of the developed LFIA system was 0.138 ng/mL. The area under the curve of this system was calculated as 0.852. The system did not show any false-negative result when 47 human serum samples were analyzed; it only detected PSA and did not detect alpha-fetoprotein and newborn calf serum in the samples. Additionally, fluorescence was maintained on the strip for 10 d after the test. With its high sensitivity and convenience, the devised LFIA kit can be used for the diagnosis of prostate cancer.

Quantum dots' size matters for balancing their quantity and quality in label materials to improve lateral flow immunoassay performance for C-reactive protein determination

Incorporating quantum dots (QDs) into dendritic mesoporous silica nanoparticles (DMSNs) for signal amplification of label materials represents an efficient strategy to improve the performance of lateral flow immunoassays (LFIAs). In this work, it is found that the CdSe/ZnS QD's size matters for balancing their loading amount and quantum yields (QYs) in the DMSNs-QDs based label materials and ultimately determining the performance of LFIA. The impacts of three CdSe/ZnS QDs with diameters of 9.1, 10.5 and 11.7 nm on CdSe/ZnS QDs incorporation and LFIA applications are studied. The increase of CdSe/ZnS QDs size from 9.1 to 11.7 nm results in a decrease in CdSe/ZnS QDs loading amount and an increase in QYs of incorporated CdSe/ZnS QDs. This trade-off leads to an optimized CdSe/ZnS QDs size of 10.5 nm, which exhibits the best LFIA performance due to the balanced QDs loading (2.26 g g^-1) and QY (57.1%). The 10.5 nm CdSe/ZnS QDs incorporated DMSNs-QDs for C-reactive protein (CRP) detection achieved a limit of detection of 5 pg mL^-1 (equivalent to 4.2 × 10^-14 M) with naked eye, which is lower than literature reports and commercial LFIA products. This study demonstrates that the CdSe/ZnS QD's size matters for improving the quality of DMSNs-QDs and their LFIA performance for CRP determination, providing new insights into the rational design of advanced label materials for improving LFIA performance.

A label-free fluorescent aptasensor based on HCR and G-quadruplex DNAzymes for the detection of prostate-specific antigen

Prostate specific antigen (PSA) has been considered as the most potential serological biomarker for the early stage detection of prostate cancer. Here, a label-free fluorescence aptasensing strategy for detecting PSA based on hybridization chain reaction (HCR) and G-quadruplex DNAzymes has been developed. This designed strategy consists of three DNA probes, aptamer probe (AP), hairpin probe 1 (H1) and hairpin probe 2 (H2). In the presence of target PSA, the aptamer sequences in AP specifically recognized PSA to form a PSA-aptamer complex, causing an AP conformation change and thus releasing the initiator, which triggered the chain-like assembly of H1 and H2 that yielded extended nicked double-stranded DNA through HCR. Upon the addition of hemin, the G-rich segments at the end of H1 and H2 self-assembled into the peroxidase-mimicking hemin/G-quadruplex DNAzymes, which catalyzed the hydrogen peroxide-mediated oxidation of thiamine to give a fluorescence signal dependent on the concentration of PSA. Under optimal conditions, a limit of detection of 0.05 nM and a linear range from 0.1 nM to 1 nM (R2 = 0.9942) were achieved by this assay. In addition, other interfering proteins, such as IgG, AFP and CEA, did not produce any significant change in the fluorescence intensity response, indicating good selectivity of this sensor for PSA detection. Finally, this proposed aptasensor was successfully used for diluted serum samples.

Rational Design of Dendritic Mesoporous Silica Nanoparticles' Surface Chemistry for Quantum Dot Enrichment and an Ultrasensitive Lateral Flow Immunoassay

Lateral flow immunoassays (LFIAs) have drawn much attention in point-of-care diagnostic applications, and the development of high-performance label materials is the key. In this study, the impact of the surface chemistry of dendritic mesoporous silica nanoparticles (DMSNs) on their enrichment performance toward quantum dots (QDs) and signal amplification of the resultant DMSNs-QDs as label materials have been investigated. A series of DMSNs with controllable amino/thiol group densities have been synthesized. It is demonstrated that the amino groups are beneficial for QD fluorescence preservation, owing to the amino-based surface passivation, while the thiol groups are responsible for increasing the loading capacity of QDs due to the thiol-metal coordination. The optimized DMSNs-QDs labels with an amino density of 153 μmol g^-1 and a thiol density of 218 μmol g^-1 displayed sufficient QD fluorescence preservation (89.4%) and high QD loading capacity (1.55 g g^-1). Ultrasensitive detection of serum amyloid A (SAA) with a detection limit of 10 pg mL^-1 with the naked eye was achieved, which is 1 order of magnitude higher than that reported in the literature. This study provides insights into the development of advanced label materials and an ultrasensitive LFIA for future bioassay applications.

Au-Ag assembled on silica nanoprobes for visual semiquantitative detection of prostate-specific antigen

Background

Blood prostate-specific antigen (PSA) levels are widely used as diagnostic biomarkers for prostate cancer. Lateral-flow immunoassay (LFIA)-based PSA detection can overcome the limitations associated with other methods. LFIAbased PSA detection in clinical samples enables prognosis and early diagnosis owing to the use of high-performance signal reporters.

Results

Here, a semiquantitative LFIA platform for PSA detection in blood was developed using Au–Ag nanoparticles (NPs) assembled on silica NPs (SiO2@Au–Ag NPs) that served as signal reporters. Synthesized SiO2@Au–Ag NPs exhibited a high absorbance at a wide wavelength range (400–800 nm), with a high scattering on nitrocellulose membrane test strips. In LFIA, the color intensity of the test line on the test strip differed depending on the PSA concentration (0.30–10.00 ng/mL), and bands for the test line on the test strip could be used as a standard. When clinical samples were assessed using this LFIA, a visual test line with particular color intensity observed on the test strip enabled the early diagnosis and prognosis of patients with prostate cancer based on PSA detection. In addition, the relative standard deviation of reproducibility was 1.41%, indicating high reproducibility, and the signal reporter showed good stability for 10 days.

Conclusion

These characteristics of the signal reporter demonstrated the reliability of the LFIA platform for PSA detection, suggesting potential applications in clinical sample analysis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00817-4.

Preparation of “pomegranate”-like QD/SiO2/poly(St-co-MAA) fluorescent nanobeads in two steps to improve stability and biocompatibility

Fluorescent nanobeads are widely used due to their advantages of visualization, sensitivity and the quantitative measurement of target analytes.

Background-Free Chromatographic Detection of Sepsis Biomarker in Clinical Human Serum through Near-Infrared to Near-Infrared Upconversion Immunolabeling

Luminescence nanomaterial-based lateral flow assay (LFA) is promising for point-of-care tests. However, the detection sensitivity and accuracy are often affected by the interferences of autofluorescence and photon scattering from nitrocellulose membrane and colored plasma. Here, we describe a near-infrared to near-infrared upconversion nanoparticle (UCNP) immunolabeled LFA for background-free chromatographic detection of sepsis biomarker procalcitonin (PCT) in clinical human plasma. This upconversion immunolabeling enables both light excitation (at ∼980 nm) and anti-Stokes emission (at 800 nm) to be adopted within the first biological window (700-1000 nm), which eliminates background autofluorescence as well as photon scattering interferences, empowering a high-sensitivity detection without complicated procedures. After optimization, the described assay presented a limit of detection reaching down to 0.03 ng/mL, lower than the normal level (0.05 ng/mL), while having a detection range of 0.03-50 ng/mL that covers the clinical PCT level of interest (0.5-10 ng/mL). The assay recoveries in human serum samples were evaluated to be about 95-110%, whereas the inter- and intra-assay coefficient variations were both determined to be below 15%. Importantly, measured PCT concentrations in clinical samples are in good correlation with that of the electrochemiluminescence immunoassay (Roche) widely applied in large clinical settings. This near-infrared to near-infrared upconversion immunolabeling approach has direct implications for ultrasensitive and background-free point-of-care detection of other serum biomarkers in resource-limited clinical settings.

Advantages of Lateral Flow Assays Based on Fluorescent Submicrospheres and Quantum Dots for Clostridium difficile Toxin B Detection

Clostridium difficile colitis is caused by a cytotoxin produced by the anaerobic bacteria C. difficile in the epithelial cells of the large intestine, particularly C. difficile toxin B (TcdB). However, the sensitivity of currently utilized C. difficile endotoxin determination methods has been called into question, and, therefore, more accurate and convenient detection methods are needed. Our study is the first to systematically compare fluorescent submicrosphere-based and quantum-dot nanobead-based lateral fluidity measurement methods (FMs-LFA and QDNBs-LFA) with toxin B quantification in fecal samples via sandwich analysis. The limits of detection (LOD) of FMs-LFA and QDNBs-LFA in the fecal samples were 0.483 and 0.297 ng/mL, respectively. TcdB analyses of the fecal samples indicated that the results of QDNBs-LFA and FMs-LFA were consistent with those of a commercial enzyme-linked immunosorbent assay (ELISA) test kit. The sensitivity of QDNBs-LFA was highly correlated with clinical diagnoses. Therefore, quantum dot nanobeads (QDNBs) are deemed highly suitable for lateral fluidity analyses, which would facilitate the implementation of portable and rapid on-the-spot applications, such as food hygiene and safety tests and onsite medical testing.

Gold nanostars-enhanced Raman fingerprint strip for rapid detection of trace tetracycline in water samples

Rapid and accurate detection of antibiotics at trace levels in food represents a great challenge. Tetracycline (TC), as a sort of broad-spectrum antibiotic, has been extensively used in animal infection therapy and animal husbandry as growth promoters. Large amounts of TC residues in animal-derived foods affect food quality and safety, and cause undesirable side effects such as allergic reactions and bacterial antibiotic resistance. Here, a Raman fingerprint strip sensor was reported based on surface-enhanced Raman scattering technology and demonstrated for ultrasensitive detection of TC. In this approach, 4-aminothiophenol (4-ATP) modified gold nanostars (GNSs) were used as a strong Raman reporter, which was coated with anti-TC monoclonal antibody serving as a biorecognition to acquire both visual and Raman signals on the test line. To demonstrate the performance of this strip, TC standard solutions with concentrations ranging from 0.5 to 50 ng/mL was detected, the limit of the detection (LOD) for the Raman signal was 0.04 ng/mL, which was 100 times more sensitive than those of color intensity quantifications. The other analogues, oxytetracycline, and chlortetracycline were detected using this method, making them suitable for the samples with TC analogues screening.

Quantum Dot Bioconjugates for Diagnostic Applications

Quantum dots (QDs) are a special type of engineered nanomaterials with outstanding optoelectronic properties that make them as a very promising alternative to conventional luminescent dyes in biomedical applications, including biomolecule (BM) targeting, luminescence imaging and drug delivery. A key parameter to ensure successful biomedical applications of QDs is the appropriate surface modification, i.e. the surface of the nanomaterials should be modified with the appropriate functional groups to ensure stability in aqueous solutions and it should be conjugated with recognition elements capable of ensuring an efficient tagging of the BMs of interest. In this review we summarize the most relevant strategies used for surface modification of QDs and for their conjugation to BMs in preparation of their application in nanoplatforms for luminescent BM sensing and imaging-guided targeting. The applications of conjugations of photoluminescent QDs with different BMs in both in vitro and in vivo chemical sensing, immunoassays or luminescence imaging are reviewed. Recent progress in the application of functionalized QDs in ultrasensitive detection in bioanalysis, diagnostics and imaging strategies are reported. Finally, some key future research goals in the progress of bioconjugation of QDs for diagnosis are identified, including novel synthetic approaches, the need for exhaustive characterization of bioconjugates and the design of signal amplification schemes.

Merging new-age biomarkers and nanodiagnostics for precision prostate cancer management

The accurate identification and stratified treatment of clinically significant early-stage prostate cancer have been ongoing concerns since the outcomes of large international prostate cancer screening trials were reported. The controversy surrounding clinical and cost benefits of prostate cancer screening has highlighted the lack of strategies for discriminating high-risk disease (that requires early treatment) from low-risk disease (that could be managed using watchful waiting or active surveillance). Advances in molecular subtyping and multiomics nanotechnology-based prostate cancer risk delineation can enable refinement of prostate cancer molecular taxonomy into clinically meaningful and treatable subtypes. Furthermore, the presence of intertumoural and intratumoural heterogeneity in prostate cancer warrants the development of novel nanodiagnostic technologies to identify clinically significant prostate cancer in a rapid, cost-effective and accurate manner. Circulating and urinary next-generation prostate cancer biomarkers for disease molecular subtyping and the newest complementary nanodiagnostic platforms for enhanced biomarker detection are promising tools for precision prostate cancer management. However, challenges in merging both aspects and clinical translation still need to be overcome.

Near-Infrared Lanthanide-Doped Nanoparticles for a Low Interference Lateral Flow Immunoassay Test

The lateral flow immunoassay test (LFT), as a method of a point of care test, is widely used in disease diagnosis, food security, and environment observation due to its portability and testing rapidity. A fluorescence lateral flow immunoassay was developed recently to enhance the sensitivity and accuracy of the LFT. However, for most fluorescence reporters, their emission and excitation wavelengths are located in the ultraviolet or visible region. Serum or whole blood significantly absorbs and scatters light of this region, and this will result in background signal interference. In this study, we replace traditional fluorescence reporters with near-infrared lanthanide-doped nanoparticles (NIR-RENPs) to establish a NIR-LFT platform. Blood and other biological samples scatter and absorb less near-infrared light than visible light, and the autofluorescence of biological samples is rarely located in this region. Therefore, using NIR light as a signal can diminish the interference of background noise and suffer from less signal attenuation. In addition, compared with commonly used NIR organic dye, NIR-RENPs have better stability. It is promising that lateral flow immunoassays based on NIR lanthanide-doped nanoparticles are able to acquire a lower detection limit and better accuracy, and they are more suitable for application in commercial settings.

A multicolor multiplex lateral flow assay for high-sensitivity analyte detection using persistent luminescent nanophosphors

Incorporating two persistent luminescent nanophosphors (PLNPs), green-emitting SrAl2O4:Eu2+,Dy3+ (SAO) and blue-emitting (Sr0.625Ba0.375)2MgSi2O7:Eu2+,Dy3+ (SBMSO), in a single lateral flow assay (LFA) establishes a luminescence-based, multiplex point-of-need test capable of simultaneously detecting two different analytes in a single sample. The advantages of this system are the high sensitivity and photostability of PLNPs, while only requiring access to minimal hardware and a smartphone for signal detection. The PLNPs were obtained by first wet milling bulk synthesized phosphor powders, followed by fractionation using differential centrifugal sedimentation to obtain monodisperse nanoparticles. A modified Stöber process was then employed to encapsulate the nanoparticles in a water-stable silica shell followed by attaching antibodies to the particles' surfaces using reductive amination chemistry. The resulting PLNPs were incorporated in an LFA to concurrently detect two independent model analytes, prostate-specific antigen (PSA) and human chorionic gonadotropin (hCG). The multicolor-multiplex PLNP-based assays were finally imaged using a smartphone-based imaging system with excellent detection limits (0.1 ng mL-1 of PSA and 1 ng mL-1 of hCG) that are competitive with commercially available LFAs.

A fluorescent nanosphere-based immunochromatography test strip for ultrasensitive and point-of-care detection of tetanus antibody in human serum

Tetanus still possesses a high infection risk and leads a number of human deaths in poor nations. Point-of-care and ultrasensitive detection of tetanus antibody levels in serum is the key to decrease the risk of tetanus infection and improve the health of people. In this work, by using ultra bright fluorescent nanospheres (FNs) and portable lateral flow test strip (LFTS), a point-of-care and ultrasensitive sensing method has been developed for the detection of tetanus antibodies in human serum. This assay works quite well for tetanus antibodies in the concentration range from 0.0002 to 0.0220 IU/mL with a low detection limit of 0.00011 IU/mL, which is 100-fold lower than conventional gold-based LFTSs. The high sensitivity makes this method suitable for use to detect the low-abundant target in real samples. Besides, this cost-effective FN-based LFTS assay possesses good selectivity, high accuracy, and satisfactory reliability, which holds great potential as a robust candidate for routine medical diagnosis and rapid home testing. Graphical abstract.

Ultrasensitive Detection of Severe Fever with Thrombocytopenia Syndrome Virus Based on Immunofluorescent Carbon Dots/SiO2 Nanosphere-Based Lateral Flow Assay

Sensitive detection of severe fever with thrombocytopenia syndrome virus (SFTSV) by a point-of-care assay is of great significance for promoting clinical diagnosis. In this work, ultrasensitive detection of SFTSV was achieved by using fluorescent carbon dots/SiO2 nanospheres (CSNs) as reporters for a lateral flow assay. The prepared CSNs were resistant to extreme environments and had strong stability. The uniform CSNs with the size of about 200 nm were obtained by differential centrifugation. Their absolute quantum yields in the aqueous and solid phases are 56.3 and 36.6%, respectively. The excellent fluorescent properties of CSNs make the test strips more sensitive and have a longer assay lifetime. Thus, the visual detection limit of the lateral flow test strip based on immunofluorescent CSN (iCSN) was as low as 10 pg/mL SFTSV nucleoprotein. The sensitivity of this assay is 2 orders of magnitude higher than that of the colloidal gold-based lateral flow test strip. Besides, the assay owns good reproducibility and high specificity. Then, iCSN-based lateral flow test strips were evaluated in real samples of human serum of patients with satisfactory results. Furthermore, this assay has a general prospect for other fluorescent immunochromatography applications.

FRET-Created Traffic Light Immunoassay Based on Polymer Dots for PSA Detection

There have been enormous efforts for developing the next generations of fluorometric lateral flow immunochromatographic strip (ICTS) owing to the great advances in fluorescent materials in these years. Here we developed one type of fluorometric ICTS based on ultrabright semiconducting polymer dots (Pdots) in which the traffic light-like signals were created by energy transfer depending on the target concentration. This platform was successfully applied for qualitatively rapid screening and quantitatively precise analysis of prostate-specific antigen (PSA) in 10 min from merely one drop of the whole blood sample. This FRET-created traffic light ICTS possesses excellent specificity and an outstanding detection sensitivity of 0.32 ng/mL for PSA. Moreover, we conducted proof-of-concept experiments to demonstrate its potential for multiplexed detection of cancer biomarkers at the same time in an individual test strip by taking advantage of the traffic light signals. To the best of our knowledge, it is the first model of a traffic light-like immunoassay test strip based on Pdots with multiplexing ability. These results would pave an avenue for designing the next generation of point-of-care diagnostics.

Dual-color magnetic-quantum dot nanobeads as versatile fluorescent probes in test strip for simultaneous point-of-care detection of free and complexed prostate-specific antigen

Simultaneous detection of free and complexed prostate-specific antigen (f-PSA and c-PSA) is critical to the prostate cancer (PCa) diagnostic accuracy for clinical samples with PSA values in the diagnostic gray zone between 4 and 10 ng mL^-1. Herein, red and green magnetic-quantum dot nanobeads (MQBs) with superior magnetic property and high luminescence were fabricated via polyethyleneimine-mediated electrostatic adsorption of numerous quantum dots onto superparamagnetic Fe₃O₄ magnetic cores, and were conjugated with f-PSA antibody and c-PSA antibody, respectively, as versatile fluorescent probes in test strip for immune recognition, magnetic enrichment, and simultaneous detection of f-PSA and c-PSA analytes in complex biological matrix with t-PSA antibody on the test line. A low-cost and portable smartphone readout device with an application was also developed for the imaging of dual-color test strips and data processing. This assay can simultaneously detect f-PSA and c-PSA with the limits of detection of 0.009 ng mL^-1 and 0.087 ng mL^-1, respectively. Clinical serum samples of PCa and benign prostatic hyperplasia patients were evaluated to confirm the clinical feasibility. The results suggest that the proposed dual-color MQBs-based fluorescent lateral flow immunoassay is a promising point-of-care diagnostics technique for the accurate diagnosis of PCa even in resource-limited settings.

Visual detection of the prostate specific antigen via a sandwich immunoassay and by using a superwettable chip coated with pH-responsive silica nanoparticles

A pH-responsive superwettable chip is described whose surface can switch between superhydrophobic and superhydrophilic. It can be used for the visual detection of the prostate specific antigen (PSA) based on contact angle readout. Magnetic beads were modified with primary antibody against PSA. After immunobinding, gold nanoparticles loaded with secondary antibody labeled with glucose oxidase is added. On addition of glucose, gluconic acid is formed which causes a drop in the local pH value. This results in a wettability switch of the pH-responsive superwettable chip from hydrophobic to hydrophilic. Under the optimized conditions, PSA can be quantified with a 3.2 pg mL^-1 limit of detection by analyzing the contact angle and the related color that changes from blue via orange to red. The method is applicable to PSA detection in serum samples and for visual classification by cancer patients and healthy persons. It is also suitable for color-blind and color-weak individuals. Conceivably, this kind of assay can be transferred to the determination of various kinds of other bioanalytes including nucleotide, proteins, and even of ions and small organic molecules, and thus is has a wide scope. Graphical abstract Schematic presentation of a pH-responsive superwettable chip coated with silica nanoparticles for the visual detection of prostate specific antigen (PSA) by reading the contact angle. The superwettable chip achieves reliable clinical detection of serum PSA from prostate cancer patients.