Improved performance of lateral flow immunoassays for alpha-fetoprotein and vanillin by using silica shell-stabilized gold nanoparticles

New Frontiers for the Early Diagnosis of Cancer: Screening miRNAs Through the Lateral Flow Assay Method

MicroRNAs (miRNAs), which circulate in the serum and plasma, play a role in several biological processes, and their levels in body fluids are associated with the pathogenesis of various diseases, including different types of cancer. For this reason, miRNAs are considered promising candidates as biomarkers for diagnostic purposes, enabling the early detection of pathological onset and monitoring drug responses during therapy. However, current methods for miRNA quantification, such as northern blotting, isothermal amplification, RT-PCR, microarrays, and next-generation sequencing, are limited by their reliance on centralized laboratories, high costs, and the need for specialized personnel. Consequently, the development of sensitive, simple, and one-step analytical techniques for miRNA detection is highly desirable, particularly given the importance of early diagnosis and prompt treatment in cases of cancer. Lateral flow assays (LFAs) are among the most attractive point-of-care (POC) devices for healthcare applications. These systems allow for the rapid and straightforward detection of analytes using low-cost setups that are accessible to a wide audience. This review focuses on LFA-based methods for detecting and quantifying miRNAs associated with the diagnosis of various cancers, with particular emphasis on sensitivity enhancements achieved through the application of different labels and detection systems. Early, non-invasive detection of these diseases through the quantification of tailored biomarkers can significantly reduce mortality, improve survival rates, and lower treatment costs.

Rapid Detection of Alpha-Fetoprotein (AFP) with Lateral Flow Aptasensor

We present a lateral flow aptasensor for the visual detection of alpha-fetoprotein (AFP) in human serum. Leveraging the precise molecular recognition capabilities of aptamers and the distinct optical features of gold nanoparticles, a model system utilizing AFP as the target analyte, along with a pair of aptamer probes, is implemented to establish proof-of-concept on standard lateral flow test strips. It is the first report of an antibody-free lateral flow assay using aptamers as recognition probes for the detection of AFP. The analysis circumvents the numerous incubation and washing steps that are typically involved in most current aptamer-based protein assays. Qualitative analysis involves observing color changes in the test area, while quantitative data are obtained by measuring the optical response in the test zone using a portable strip reader. The biosensor exhibits a linear detection range for AFP concentrations between 10 and 100 ng/mL, with a minimum detection limit of 10 ng/mL. Additionally, it has been successfully applied to detect AFP in human serum samples. The use of aptamer-functionalized gold nanoparticle probes in a lateral flow assay offers great promise for point-of-care applications and fast, on-site detection.

Dendritic mesoporous silica loaded with gold nanoclusters and their application in immunochromatographic assay

Novel green-emitting fluorescent microspheres (GreFMPs) were assembled by loading highly luminescent gold nanoclusters (Arg/ATT/AuNCs) on dendritic mesoporous silica nanoparticles (DMSNs) via PEI-mediated electrostatic adsorption. The fluorescence microspheres  exhibit excellent monodispersion with average diameters about (254.5 ± 34.6 nm). Compared with free Arg/ATT/AuNCs, the GreFMPs have similar fluorescent properties and biocompatibility but superior environmental tolerance. Subsequently, an immunochromatographic assay based on GreFMPs (GreFMP-ICA) has been successfully developed, which is highly selective toward alpha fetoprotein (AFP) in human serum. Under the optimal parameters, there is a good linear range between 0.5 and 160.0 ng/mL, the limit of detection was found to be about 0.5 ng/mL, and the recovery and relative standard deviation are 81.0 ~ 100.6% and 3.5 ~ 16.6%, respectively. These results manifested that the GreFMPs are beneficial for the rational design of the ICA platform, and the proposed GreFMP-ICA has the potential to screen AFP in clinical applications.

A Route to the Colorimetric Detection of Alpha-Fetoprotein Based on a Smartphone

Alpha-fetoprotein (AFP) is a key marker for early cancer detection and assessment. However, the current detection methods struggle to balance accuracy with the need for decentralized medical treatment. To address this issue, a new AFP analysis platform utilizing digital image colorimetry has been developed. Functionalized gold nanoparticles act as colorimetric agents, changing from purple-red to light gray-blue when exposed to different AFP concentrations. A smartphone app captures these color changes and calculates the AFP concentration in the sample. To improve detection accuracy, a hardware device ensures uniform illumination. Testing has confirmed that this system can quantitatively analyze AFP using colorimetry. The limit of detection reached 0.083 ng/mL, and the average accuracy reached 90.81%. This innovative method enhances AFP testing by offering portability, precision, and low cost, making it particularly suitable for resource-limited areas.

Recent Advances in Lateral Flow Assays for Viral Protein Detection with Nanomaterial-Based Optical Sensors

Controlling the progression of contagious diseases is crucial for public health management, emphasizing the importance of early viral infection diagnosis. In response, lateral flow assays (LFAs) have been successfully utilized in point-of-care (POC) testing, emerging as a viable alternative to more traditional diagnostic methods. Recent advancements in virus detection have primarily leveraged methods such as reverse transcription-polymerase chain reaction (RT-PCR), reverse transcription-loop-mediated isothermal amplification (RT-LAMP), and the enzyme-linked immunosorbent assay (ELISA). Despite their proven effectiveness, these conventional techniques are often expensive, require specialized expertise, and consume a significant amount of time. In contrast, LFAs utilize nanomaterial-based optical sensing technologies, including colorimetric, fluorescence, and surface-enhanced Raman scattering (SERS), offering quick, straightforward analyses with minimal training and infrastructure requirements for detecting viral proteins in biological samples. This review describes the composition and mechanism of and recent advancements in LFAs for viral protein detection, categorizing them into colorimetric, fluorescent, and SERS-based techniques. Despite significant progress, developing a simple, stable, highly sensitive, and selective LFA system remains a formidable challenge. Nevertheless, an advanced LFA system promises not only to enhance clinical diagnostics but also to extend its utility to environmental monitoring and beyond, demonstrating its potential to revolutionize both healthcare and environmental safety.

Development of lectin-based lateral flow assay for fucosylated alpha-fetoprotein

Fucosylated alpha-fetoprotein (AFP-L3) is a more specific and sensitive biomarker for early diagnosis of hepatocellular carcinoma (HCC) than only the alpha-fetoprotein (AFP) level. Rapid and simple detection of AFP-L3 level greatly facilitates the early detection as well as the treatment of HCC, resulting in the reduction of mortality. Here, we developed a rapid and sensitive lateral flow assay (LFA) using lectin Lens culinaris agglutinin (LCA), which has a specific affinity to AFP-L3 fraction of AFP, as a biorecognition element for determination of the fucosylation of AFP. The assay is based on a sandwich format performed on a lateral flow test strip. LCA was immobilized on the membrane as a test line (T). Quantitative detection of AFP-L3 was achieved by measuring the green color intensity of captured gold nanoparticle conjugates on the T and control line (C) utilizing an in-house test strip reader. The calculated absorbance obtained by the green color intensity signals proportionally increased with AFP concentrations. The developed lectin-based LFA provided a detection limit of 0.8 ng/mL for AFP with a linear range between 1.5 and 160.0 ng/mL within an assay time of 10 min. Recoveries between 74.5% and 113.2% with relative standard deviations of 5.2%-8.7% for measuring spiked human serum were also achieved. The results reveal that the proposed assay offers a rapid, sensitive, and specific method, which is useful for development in point-of-care testing for early detection and treatment of HCC.

Recent Trends in Lateral Flow Immunoassays with Optical Nanoparticles

Rapid, accurate, and convenient diagnosis is essential for effective disease management. Various detection methods, such as enzyme-linked immunosorbent assay, have been extensively used, with lateral flow immunoassay (LFIA) recently emerging as a major diagnostic tool. Nanoparticles (NPs) with characteristic optical properties are used as probes for LFIA, and researchers have presented various types of optical NPs with modified optical properties. Herein, we review the literature on LFIA with optical NPs for the detection of specific targets in the context of diagnostics.

Lanthanum nickelate spheres embedded acid functionalized carbon nanofiber composite: An efficient electrocatalyst for electrochemical detection of food additive vanillin

Contemporary food marketing is ruined by flavor enhancers rather than emphasizing the nutritional value of food. Vanillin is an overexploited flavor enhancer added to food items, thereby necessitating its detection. In this study, an electrochemical sensor was designed using a modified electrode made up of La2NiO4 functionalized carbon nanofiber (f-CNF) to effectively detect vanillin in food samples. To confirm the successful formation of La2NiO4/f-CNF, structural and morphological studies were performed using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Further electrochemical analysis was performed using cyclic voltammetry and differential pulse voltammetry techniques, which resulted in high sensitivity (0.2899 µA·μM-1·cm-2) and low limit of detection (LOD) (6 nM). This modified electrode material was tested in food samples, which showed an excellent response with recovery percentage and is a promising electrocatalyst for vanillin detection.

Chiral inorganic nanomaterials for biological applications

Chiral nanomaterials in biology play indispensable roles in maintaining numerous physiological processes, such as signaling, site-specific catalysis, transport, protection, and synthesis. Like natural chiral nanomaterials, chiral inorganic nanomaterials can also be established with similar size, charge, surface properties, and morphology. However, chiral inorganic nanomaterials usually exhibit extraordinary properties that are different from those of organic materials, such as high g-factor values, broad distribution range, and symmetrical mirror configurations. Because of these unique characteristics, there is great potential for application in the fields of biosensing, drug delivery, early diagnosis, bio-imaging, and disease therapy. Related research is summarized and discussed in this review to showcase the bio-functions and bio-applications of chiral inorganic nanomaterials, including the construction methods, classification and properties, and biological applications of chiral inorganic nanomaterials. Moreover, the deficiencies in existing studies are noted, and future development is prospected. This review will provide helpful guidance for constructing chiral inorganic nanomaterials with specific bio-functions for problem solving in living systems.

Preparation and properties of boron affinity molecularly imprinted mesoporous polymers based on Mn-doped ZnS quantum dots

Sialic acid (SA), known as N-acetyl neuraminic acid, is a natural 9-carbomonosaccharide derivative. SA has been widely applied in the early diagnosis of diseases as therapeutic target. However, the abundance of SA is very low in biological samples, which is usually interfered by the similar molecules coexisting at high abundance. Combining the advantages of high selectivity and specificity of molecularly imprinted technology, high specific surface area of mesoporous materials and excellent optical properties of quantum dots, we chose Mn-doped ZnS quantum dots as signal elements, and sialic acid as the template molecule. KH-4-MAPB with recognition ability to SA was synthesized by one-step hydrothermal method using thiolene click reaction as functional monomer. Based on the principle of boron affinity, molecularly imprinted polymers with highly ordered mesoporous structure were prepared, and the structure and fluorescence properties of fluorescent molecularly imprinted polymers were studied. FT-IR, XRD, TEM and nitrogen adsorption-desorption experiments were used to characterize the structure and morphology of the molecularly imprinted polymers. The results showed that the prepared molecularly imprinted polymers had highly ordered mesoporous structure and a large number of imprinted holes, which ensured the specific selectivity of the molecularly imprinted polymers. The fluorescence properties of MIMPs were characterized and analyzed by fluorescence spectra, equilibrium adsorption kinetics experiments were conducted and imprinting properties were recorded under different pH. The above experimental results showed that the fluorescence quenching was successfully achieved when the template molecule SA was captured by the molecularly imprinted polymer. When the concentration of SA was 1.25-100 × 10^-2 g/L, the fluorescence quenching degree of MIMPs showed a fine linear relationship with SA. The correlation coefficient was 0.9946, and the detection equation was F₀/F - 1 = 0.0215 [CSA] + 0.0241. MIMPs had a high recognition ability for SA, and the imprinting factor was 2.44. As a fluorescent sensor for SA, the response time of MIMPs was 20 min. When the buffer solution pH was 7, the imprinting factor was the largest. Under the best conditions, MIMPs revealed good selectivity and specificity for the fluorescence recognition of SA. MIMPS were also applied to the analysis of SA in real human serum samples with satisfactory results.

Recent advances in nanotechnology-enhanced biosensors for α-fetoprotein detection

α-Fetoprotein (AFP) is a kind of fetal protein that is related to tumor, the increasing concentration of which gives birth to a large variety of diseases, such as liver cancer. Therefore, the detection method with super sensitivity, high selectivity, and less time consumption under trace concentrations in early stage of diseases is becoming a necessity. In recent years, nanomaterials have been regarded as significant resources for the exploration of efficient biosensors with high sensitivity, selectivity, speed, as well as simple process, due to their excellent optical, electrical, and chemical properties. In this paper, we reviewed the research progress of AFP biosensors with enhanced sensitivity and selectivity by nanoparticles. Representative examples have also been displayed in this paper to expound the nanotechnologies utilized in the early detection of AFP. Furthermore, challenges of the clinical application of AFP biosensors based on nanotechnology have been elaborated, as well as the development opportunity in this field in the future. This review provides a comprehensive overview on the various nano-biosensor for AFP detection based on functional nanotechnology.

Development of Lateral Flow Test-System for the Immunoassay of Dibutyl Phthalate in Natural Waters

The use of a large amount of toxic synthetic materials leads to an increase in the pollution of environmental objects. Phthalates are compounds structurally related to esters of phthalic acid that are widely used in the manufacturing of synthetic packaging materials as plasticizers. Their danger is conditioned by leaching into the environment and penetrating into living organisms with negative consequences and effects on various organs and tissues. This work presents the first development of lateral flow immunoassay to detect dibutyl phthalate, one of the most common representatives of the phthalates group. To form a test zone, a hapten-protein conjugate was synthesized, and gold nanoparticles conjugated with antibodies to dibutyl phthalate were used as a detecting conjugate. The work includes the preparation of immunoreagents, selectivity investigation, and the study of the characteristics of the medium providing a reliable optical signal. Under the selected conditions for the analysis, the detection limit was 33.4 ng/mL, and the working range of the determined concentrations was from 42.4 to 1500 ng/mL. Time of the assay-15 min. The developed technique was successfully applied to detect dibutyl phthalate in natural waters with recovery rates from 75 to 115%.

Ultrasensitive point-of-care biochemical sensor based on metal-AIEgen frameworks

Point-of-care (POC) biochemical sensors have found broad applications in areas ranging from clinical diagnosis to environmental monitoring. However, POC sensors often suffer from poor sensitivity. Here, we synthesized a metal-organic framework, where the ligand is the aggregation-induced emission luminogen (AIEgen), which we call metal-AIEgen frameworks (MAFs), for use in the ultrasensitive POC biochemical sensors. MAFs process a unique luminescent mechanism of structural rigidity-enhanced emission to achieve a high quantum yield (~99.9%). We optimized the MAFs to show 10²- to 10³-fold enhanced sensitivity for a hydrogel-based POC digital sensor and lateral flow immunoassays (LFIA). MAFs have a high affinity to directly absorb proteins, which can label antibodies for immunoassays. MAFs-based LFIA with enhanced sensitivity shows robust serum detection for POC clinical diagnosis.

Glycosylated gold nanoparticles in point of care diagnostics: from aggregation to lateral flow

Current point-of-care lateral flow immunoassays, such as the home pregnancy test, rely on proteins as detection units (e.g. antibodies) to sense for analytes. Glycans play a fundamental role in biological signalling and recognition events such as pathogen adhesion and hence they are promising future alternatives to antibody-based biosensing and diagnostics. Here we introduce the potential of glycans coupled to gold nanoparticles as recognition agents for lateral flow diagnostics. We first introduce the concept of lateral flow, including a case study of lateral flow use in the field compared to other diagnostic tools. We then introduce glycosylated materials, the affinity gains achieved by the cluster glycoside effect and the current use of these in aggregation based assays. Finally, the potential role of glycans in lateral flow are explained, and examples of their successful use given.

Antibody-based lateral flow (immune) assays are well established, but here the emerging concept and potential of using glycans as the detection agents is reviewed.

Recent Advances in Silica-Nanomaterial-Assisted Lateral Flow Assay

Lateral flow assays (LFAs) have attracted much attention as rapid and affordable point-of-care devices for medical diagnostics. The global SARS-CoV-2 pandemic has further highlighted the importance of LFAs. Many efforts have been made to enhance the sensitivity of LFAs. In recent years, silica nanomaterials have been used to either amplify the signal of label materials or provide stability, resulting in better detection performance. In this review, the recent progress of silica-nanomaterial-assisted LFAs is summarized. The impact of the structure of silica nanomaterials on LFA performance, the challenges and prospects in this research area are also discussed.

Aptamer-based biosensors for the diagnosis of sepsis

Sepsis, the syndrome of infection complicated by acute organ dysfunction, is a serious and growing global problem, which not only leads to enormous economic losses but also becomes one of the leading causes of mortality in the intensive care unit. The detection of sepsis-related pathogens and biomarkers in the early stage plays a critical role in selecting appropriate antibiotics or other drugs, thereby preventing the emergence of dangerous phases and saving human lives. There are numerous demerits in conventional detection strategies, such as high cost, low efficiency, as well as lacking of sensitivity and selectivity. Recently, the aptamer-based biosensor is an emerging strategy for reasonable sepsis diagnosis because of its accessibility, rapidity, and stability. In this review, we first introduce the screening of suitable aptamer. Further, recent advances of aptamer-based biosensors in the detection of bacteria and biomarkers for the diagnosis of sepsis are summarized. Finally, the review proposes a brief forecast of challenges and future directions with highly promising aptamer-based biosensors.

Highly Sensitive and Selective Photoelectrochemical Aptasensors for Cancer Biomarkers Based on MoS2/Au/GaN Photoelectrodes

An Au/GaN photoelectrode was prepared by sputtering 30 nm thick Au film on the surface of n-type gallium nitride (GaN). When the electrode contacts with multilayered molybdenum disulfide (MoS₂), photogenerated electrons and photogenerated holes transfer to MoS₂ because of the band gap matching of MoS₂ and GaN. The presence of Au promotes charge transfer and results in a greater recombination of electrons and holes; by this means, a more significant suppression of photocurrent can be detected. This characteristic has been coupled with the high selectivity of an aptamer and applied to develop a novel photoelectrochemical aptasensor for cancer biomarkers (alpha-fetoprotein (AFP) as a model). The aptamer of AFP was modified on the surface of the Au/GaN photoelectrode by Au-S bonds, which can bind to the target protein with high selectivity. Then, the transfer process of the charge carriers of GaN to MoS₂ can be blocked by the target protein so that the suppression of photocurrent is reduced. The difference of the photocurrent in the presence and absence of AFP (ΔI) showed a linear relationship with AFP concentration that ranged from 1.0-150 ng/mL (R² = 0.9995), and the detection limit was 0.3 ng/mL. The standard addition recovery rates ranged from 85.2 to 91.7%. The method possessed good sensitivity and high selectivity for AFP detection. The developed biosensor can be modified to detect other cancer biomarkers by simply replacing the aptamer used.

Ultrasensitive and Highly Specific Lateral Flow Assays for Point-of-Care Diagnosis

Lateral flow assays (LFAs) are paper-based point-of-care (POC) diagnostic tools that are widely used because of their low cost, ease of use, and rapid format. Unfortunately, traditional commercial LFAs have significantly poorer sensitivities (μM) and specificities than standard laboratory tests (enzyme-linked immunosorbent assay, ELISA: pM-fM; polymerase chain reaction, PCR: aM), thus limiting their impact in disease control. In this Perspective, we review the evolving efforts to increase the sensitivity and specificity of LFAs. Recent work to improve the sensitivity through assay improvement includes optimization of the assay kinetics and signal amplification by either reader systems or additional reagents. Together, these efforts have produced LFAs with ELISA-level sensitivities (pM-fM). In addition, sample preamplification can be applied to both nucleic acids (direct amplification) and other analytes (indirect amplification) prior to LFA testing, which can lead to PCR-level (aM) sensitivity. However, these amplification strategies also increase the detection time and assay complexity, which inhibits the large-scale POC use of LFAs. Perspectives to achieve future rapid (<30 min), ultrasensitive (PCR-level), and "sample-to-answer" POC diagnostics are also provided. In the case of LFA specificity, recent research efforts have focused on high-affinity molecules and assay optimization to reduce nonspecific binding. Furthermore, novel highly specific molecules, such as CRISPR/Cas systems, can be integrated into diagnosis with LFAs to produce not only ultrasensitive but also highly specific POC diagnostics. In summary, with continuing improvements, LFAs may soon offer performance at the POC that is competitive with laboratory techniques while retaining a rapid format.

(Nano)tag-antibody conjugates in rapid tests

Antibodies (Abs) are naturally derived materials with favorable affinity, selectivity, and fast binding kinetics to the respective antigens, which enables their application as promising recognition elements in the development of various types of biosensors/bioassays, especially in rapid tests. These tests are low-cost and easy-to-use biosensing devices with broad applications including medical or veterinary diagnostics, environmental monitoring and industrial usages such as safety and quality analysis in food, providing on-site quick monitoring of various analytes, making it possible to save analysis costs and time. To reach such features, the conjugation of Abs with various nanomaterials (NMs) as tags is necessary, which range from conventional gold nanoparticles to other nanoparticles recently introduced, where magnetic, plasmonic, photoluminescent, or multi-modal properties play a critical role in the overall performance of the analytical device. In this context, to preserve the Ab affinity and provide a rapid response with long-term storage capability, the use of efficient bio-conjugation techniques is critical. Thanks to their prominent role in rapid tests, many studies have been devoted to the design and development of Abs-NMs conjugates with various chemistries including passive adsorption, covalent coupling, and affinity interactions. In this review, we present the state-of-the-art techniques allowing various Ab-NM conjugates with a special focus on the efficiency of the developed probes to be employed in in vitro rapid tests. Challenges and future perspectives on the development of Ab-conjugated nanotags in rapid diagnostic tests are highlighted along with a survey of the progress in commercially available Ab-NM conjugates.

Resonance Raman scattering-infrared absorption dual-mode immunosensing for carcinoembryonic antigen based on ZnO@SiO2 nanocomposites

Detection of cancer biomarkers is crucial for the diagnosis and monitoring of malignant tumors. However, the accuracy and sensitivity still require sufficient improvement for practically clinical application. In this work, a reliable and sensitive dual-mode immunosensing method is described for carcinoembryonic antigen (CEA) detection using a biofunctional ZnO@SiO₂ nanocomposite as a resonance Raman scattering (RRS)-infrared (IR) absorption nanoprobe. The multiphonon RRS signal originating from the ZnO and the characteristic IR fingerprint signal of the transverse optical and longitudinal optical phonon modes of the asymmetric stretching of Si-O-Si bonds showed no interference with each other. A CEA antibodies-immobilized substrate was fabricated to capture the analyte/nanoprobe complexes. The RRS intensity at 569 cm^‒1 and the IR absorption at 1061 cm^‒1 were used for quantitative analysis. Accurate CEA detection was performed as a result of the strong resistance of the dual-mode nanoprobe to surrounding interference. The limit of detection was 98.0 fg mL^‒1. The detection range was 500 ng mL^‒1 - 50 fg mL^‒1, which is wider than those of single-mode RRS or IR absorption immunosensings. High reproducibility, selectivity and specificity were achieved. The assay performance of human serum samples demonstrated the practicability of the method in clinical cancer diagnosis.

Lateral flow biosensors based on the use of micro- and nanomaterials: a review on recent developments

This review (with 187 refs.) summarizes the progress that has been made in the design of lateral flow biosensors (LFBs) based on the use of micro- and nano-materials. Following a short introduction into the field, a first section covers features related to the design of LFBs, with subsections on strip-based, cotton thread-based and vertical flow- and syringe-based LFBs. The next chapter summarizes methods for sample pretreatment, from simple method to membrane-based methods, pretreatment by magnetic methods to device-integrated sample preparation. Advances in flow control are treated next, with subsections on cross-flow strategies, delayed and controlled release and various other strategies. Detection conditionst and mathematical modelling are briefly introduced in the following chapter. A further chapter covers methods for reliability improvement, for example by adding other validation lines or adopting different detection methods. Signal readouts are summarized next, with subsections on color-based, luminescent, smartphone-based and SERS-based methods. A concluding section summarizes the current status and addresses challenges in future perspectives. Graphical abstractRecent development and breakthrough points of lateral flow biosensors.

Modification of a nitrocellulose membrane with cellulose nanofibers for enhanced sensitivity of lateral flow assays: application to the determination of Staphylococcus aureus

Lateral flow assays, as a low-cost, simple, portable and disposable product of vitro diagnostic, are being widely used for point-of-care testing. However, the poor sensitivity of LFAs is the main challenge for commercialization. In order to enhance the sensitivity of LFAs, cellulose nanofibers (CNFs) have been integrated into LFAs to enhance the sensitivity of protein LFAs. A simple method is also presented to modify the properties of paper substrate by incorporating CNFs into a nitrocellulose membrane to enhance the sensitivity of nucleic acid LFAs. This method changes the pore size, porosity, surface groups and surface area of paper substrate and then increases the adsorption ability of biomolecules on paper substrate. The results indicate that the sensitivity of nucleic acid LFAs in Staphylococcus aureus testing achieves a 20-fold enhancement. Hence, we anticipate that this simple method has the potential for other paper-based devices to improve the performance. Graphical abstractA simple method is used to modify the properties of paper substrate by incorporating cellulose nanofibers (CNFs) into nitrocellulose (NC) membrane to enhance the sensitivity of nucleic acid LFAs.

Ovalbumin antibody-based fluorometric immunochromatographic lateral flow assay using CdSe/ZnS quantum dot beads as label for determination of T-2 toxin

This work describes an anti-ovalbumin antibody-based lateral flow immunoassay (LFI) for T-2 toxin. The antibody uses a coating antigen as a bifunctional element for universality and introduces preincubation to improve the detection limits of the method. T-2 toxin and ovalbumin-modified T-2 toxin competitively binds on the anti-T-2 toxin monoclonal antibody modified on CdSe/ZnS quantum dot beads during preincubation. The modified T-2 toxin acts as a bifunctional element that forms immuno complexes during preincubation and combines with anti-ovalbumin antibody coated in the test line through the ovalbumin terminal. Fluorescence is detected at 610 nm on the test zone following photoexcitation at 365 nm. It has a reverse dose-effect relationship with the amount of T-2 toxin. The calibration plot is linear in the 20-110 fg mL^-1 T-2 toxin concentration range, and the limit of detection (LOD) is 10 fg mL^-1, which is lower by 8-fold than that of the traditional LFI system (LOD 80 fg mL^-1) and one order of magnitude than those of LFIs with labels of colloidal gold nanoparticles (LOD 150 fg mL^-1) or fluorophores (LOD 190 ng mL^-1). Universality was verified through aflatoxin B₁ detection using the established ovalbumin antibody-based LFI system (LOD 10 fg mL^-1). The performance of the method was compared with that of established systems and a commercial ELISA kit (LOD 360 fg mL^-1). Graphical abstractSchematic representation of ovalbumin antibody-based immunochromatographic lateral flow assay for T-2 toxin. Preincubation is introduced for high sensitivity. T-2- anti-ovalbumin acts as a bi-functional element for universality. CdSe/ZnS quantum dot beads act as label. Fluorometric signal is detected at 610 nm.

Microfluidic chip electrophoresis for simultaneous fluorometric aptasensing of alpha-fetoprotein, carbohydrate antigen 125 and carcinoembryonic antigen by applying a catalytic hairpin assembly

An aptamer based assay is presented that is making use of a catalytic hybrid assembly and a microfluidic chip electrophoresis format. It enables simultaneous determination of the biomarkers (BMs) α-fetoprotein (AFP), carbohydrate antigen 125 (CA125), and carcinoembryonic antigen (CEA). The respective aptamers were covalently bound to Fe₃O₄@AuNPs (AuMPs) magnetic beads and then used to capture the biomarkers on their surface. Different single-stranded DNA primers were then labeled with various antibodies as encoding and signaling tags. The signal tags reacted with AuMPs-BMs to form different antibody-BM-aptamer complexes. After magnetic separation, three pairs of hairpins as substrates were introduced to trigger catalytic hybrid assembly by the primers in the complex. This will form many duplex DNA products of different length in the supernatant. The products can be magnetically separated by microfluidic chip electrophoresis and determined by fluorometry at excitation/emission wavelengths of 495/525 nm. Several experimental conditions including the hairpin concentration, reaction time and temperature were systemically optimized. The method can simultaneously quantify AFP, CEA and CA125, respectively, with detection limits of 0.1, 0.2, 0.15 pg mL^-1 (at S/N = 3). The aptamer functionalized magnetic beads can be reused for at least 20 times with a recovery of up to 80% after heat treatment. The method was employed to simultaneously detect the three BMs in serum samples. Graphical abstract Schematic presentation of the microfluidic chip electrophoresis and antibody-aptamer based multianalysis method for simultaneous detection of alpha-fetoprotein (AFP), carbohydrate antigen 125 (CA125) and carcinoembryonic antigen (CEA).

A review on advances in methods for modification of paper supports for use in point-of-care testing

Paper is a widely used support for use in devices for point-of-care testing (POCT) in clinical diagnosis, food safety monitoring and environmental pollution. Paper is inexpensive, biocompatible, biodegradable and allows a sample fluid to flow by capillary force. Numerous method have been developed recently for chemical modification of papers in order to introduce different functionalities. This review (with 148 refs.) summarizes the recent progress in paper-based POCT devices. The introduction summarizes the state of the art of paper-based POCT devices and the physicochemical properties of existing unmodified materials (including cellulose, cellulose-based composites, cotton fibers, glass fibers, nitrocellulose, thread). Methods for paper modification for sample pretreatment are summarized next, with subsections on sample storage and collection, sample separation, nucleic acid extraction and sample preconcentration. Another main section covers approaches for paper modification for improving POCTs, with subsections on assays for proteins, nucleic acids, drugs, ion and organic molecules. The advantages and disadvantages of these approaches are compared. Several tables are presented that summarize the various modification techniques. A concluding section summarizes the current status, addresses challenges and gives an outlook on future perspectives of POCTs. Graphical abstract This review summarizes the progress that has been made in paper based point-of-care testing (POCT) and lateral flow assays (LFAs), quite often by using advanced nanomaterials for paper modification.

A semi-quantitative rapid multi-range gradient lateral flow immunoassay for procalcitonin

A rapid semi-quantitative gradient lateral flow immunoassay (LFIA) of procalcitonin (PCT), a peptide precursor of the hormone calcitonin, was developed. The method is based on particular analyte cut-offs by immobilizing specific antibodies on the test strip with a consistent (gradient) increase in concentration from line to line. Semi-quantitative multi-range analysis is evaluated visually by counting the number of colored test lines corresponding to a certain concentration range of sepsis marker: [PCT]˂0.25; 0.25 ≤ [PCT] < 0.5; 0.5 ≤ [PCT] < 2; 2 ≤ [PCT] < 10; [PCT] ≥ 10 ng·mL^-1. This multi-range gradient LFIA was implemented by using two types of label: spherical gold nanoparticles (35 nm) and hierarchical popcorn-like gold nanoparticles (100 nm). The comparison of this LFIA with an ELISA (for n = 82) yielded 87.5% and 76.6% sensitivities, and 92.3% and 92.3% specificities, respectively. Thus, multi-range gradient LFIA performs well at PCT thresholds, which is important for early diagnosis of sepsis and severe bacterial infection. In our perception, this method has a wide scope in that it may be implemented in numerous other LFIA based test systems. Graphical abstract Schematic of the gradient lateral flow immunoassay for determination of clinically relevant procalcitonin ranges. It allows to reach the correlation between the number of developed test lines and procalcitonin concentration range in serum by pre-immobilization of capture antibodies in a consistently (gradient) increasing concentration.

A fluorometric aptamer nanoprobe for alpha-fetoprotein by exploiting the FRET between 5-carboxyfluorescein and palladium nanoparticles

Alpha-fetoprotein (AFP) is a reliable clinical marker of hepatocellular carcinoma (HCC). A highly sensitive fluorometric aptamer nanoprobe is described for AFP detection. It is based on fluorescence resonance energy transfer (FRET) between AFP aptamer labelled with 5-carboxyfluorescein (FAM) and palladium nanoparticles (PdNPs). The PdNPs quench the green fluorescence of the FAM-AFP aptamer via interactions between nitrogen functional groups of the AFP aptamer and PdNPs. When AFP was introduced into the FAM-AFP aptamer-PdNPs FRET system, the AFP aptamer preferentially combines with AFP. This results in a conformational change and weakens the interaction between the aptamer and the PdNPs. Thus, the fluorescence of FAM recovers. The fluorescence recovery of FAM increases linearly in the 5.0-150 ng·mL^-1 AFP concentration range and has a 1.4 ng·mL^-1 detection limit. The assay was applied to the analysis of spiked diluted human serum. The recovery values ranged from 98.3 to 112.9%, with relative standard deviations of <1.1%. This biosensing strategy provides a reliable and ultrasensitive protocol for the quantification of biomarkers with relevant antigens and aptamers. Graphical abstract Schematic presentation of a fluorometric aptamer nanoprobe for AFP assay based on fluorescence resonance energy transfer (FRET) between AFP aptamer labelled with 5-carboxyfluorescein (FAM) and palladium nanoparticles (PdNPs).