Visual detection of thrombin using a strip biosensor through aptamer-cleavage reaction with enzyme catalytic amplification

Engineering gold nanoparticles for molecular diagnostics and biosensing

Advances in nanotechnology and medical science have spurred the development of engineered nanomaterials and nanoparticles with particular focus on their applications in biomedicine. In particular, gold nanoparticles (AuNPs) have been the focus of great interest, due to their exquisite intrinsic properties, such as ease of synthesis and surface functionalization, tunable size and shape, lack of acute toxicity and favorable optical, electronic, and physicochemical features, which possess great value for application in biodetection and diagnostics purposes, including molecular sensing, photoimaging, and application under the form of portable and simple biosensors (e.g., lateral flow immunoassays that have been extensively exploited during the current COVID-19 pandemic). We shall discuss the main properties of AuNPs, their synthesis and conjugation to biorecognition moieties, and the current trends in sensing and detection in biomedicine and diagnostics. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > In Vitro Nanoparticle-Based Sensing Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Thrombin Determination Using Graphene Oxide Sensors with Co-Assisted Amplification

Graphene oxide (GO) is widely used in sensors. The detection of proteins based on bare GO has been developed; however, the detection sensitivity needs to be improved. In this paper, a novel GO-DNA sensor for thrombin detection was developed using an aptamer linked to the surface of GO. Polyethylene glycol (PEG) was further used to prevent thrombin from nonspecific adsorption and to improve the sensitivity of the sensor for detection of thrombin. In order to improve the limit of detection for thrombin, we developed a GO and RecJf exonuclease co-assisted signal amplification strategy, and a detection limit of 24.35 fM for thrombin was achieved using this strategy. The results show that it is a promising method in analytical applications.

Development of nucleic acid aptamer-based lateral flow assays: A robust platform for cost-effective point-of-care diagnosis

Lateral flow assay (LFA) has made a paradigm shift in the in vitro diagnosis field due to its rapid turnaround time, ease of operation and exceptional affordability. Currently used LFAs predominantly use antibodies. However, the high inter-batch variations, error margin and storage requirements of the conventional antibody-based LFAs significantly impede its applications. The recent progress in aptamer technology provides an opportunity to combine the potential of aptamer and LFA towards building a promising platform for highly efficient point-of-care device development. Over the past decades, different forms of aptamer-based LFAs have been introduced for broad applications ranging from disease diagnosis, agricultural industry to environmental sciences, especially for the detection of antibody-inaccessible small molecules such as toxins and heavy metals. But commercial aptamer-based LFAs are still not used widely compared with antibodies. In this work, by analysing the key issues of aptamer-based LFA design, including immobilization strategies, signalling methods, and target capturing approaches, we provide a comprehensive overview about aptamer-based LFA design strategies to facilitate researchers to develop optimised aptamer-based LFAs.

Visual detection of kanamycin with DNA-functionalized gold nanoparticles probe in aptamer-based strip biosensor

Kanamycin has been widely used to treat human and animal diseases. The excessive use of kanamycin causes its accumulation in animal-derived foods, and eventually threats human health. In the present study, we develop a lateral flow strip biosensor for fast and sensitive detection of kanamycin. The strip biosensor combines the easy separation of magnetic microspheres (MMS) with target-mediated chain displacement of single-stranded DNA and the capture of the visible DNA-functionalized gold nanoparticles (AuNPs) probe. The presence of kanamycin can competitively bind to the aptamer and release cDNA to the supernatant. The concentration of free cDNA, which is the direct target of the strip, is proportional to the concentration of kanamycin. The capture of DNA-functionalized AuNPs on the test zone of the strip through cDNA-induced hybridization provides a visual detection signal. The assay can be completed within 20 min. The visual detection limit by naked eyes of the strip is 50 nM. A linear detection range of 5-500 nM is derived for quantitative determination, with the detection limit of 4.96 nM (S/N = 3). This lateral flow strip biosensor can quickly and sensitively detect kanamycin in different food samples, which holds great application potential in medicine and daily life.

Target-induced structure switching of aptamers facilitates strand displacement for DNAzyme recycling amplification detection of thrombin in human serum

To monitor the thrombin concentration under the condition of abnormal blood coagulation is of clinical significance for the diagnosis of various diseases. Here, on the basis of the aptamer structure switching induced by the target molecules and the signal amplification strategy via recycling of metal-ion dependent DNAzymes, we have established a sensitive and simple fluorescent aptasensor for detecting thrombin in human serum. The thrombin target specifically binds to the aptamer sequence and causes a corresponding conformational structure switching, which leads to the formation of a toehold sequence to facilitate the strand migration displacement reaction for the generation of functional metal-ion dependent DNAzymes. These DNAzymes further cleave the fluorescently quenched hairpin substrates cyclically to yield substantially amplified fluorescence recovery for sensitively detecting thrombin in the dynamic range from 0.01 nM to 50 nM. Such an aptasensor shows a detection limit of 6.9 pM and can achieve the monitoring of thrombin in diluted human serum with high selectivity, offering a universal sensing strategy for the construction of various sensitive and simple aptasensors to detect different biomarker molecules.

An aptamer-based hook-effect-recognizable three-line lateral flow biosensor for rapid detection of thrombin

In this paper, a three-line LFB was successfully developed by adding a thrombin line to a conventional two-line LFB for the detection of thrombin in a wide range of human serum. We introduced a thrombin line between the test line and the control line. The concentration of thrombin in the sample was quantitatively related to the signal formation on the three lines of the LFB. We can make use of signal on three lines to quantitative determinate the thrombin by data processing. The detection range of thrombin concentrations measured in 10 min was 1 nM to 100 μM and the LOD was 0.85 nM. Our approach paves way for rapid and sensitive thrombin detection and a superior device for testing in a wide range of physiological concentrations, which also can be used in other hook-effect-limited aptamers or antibodies based sandwich LFBs, and has a high accuracy even within the range of the hook-effect.

Using Ca-doped carbon dots as catalyst to amplify signal to determine ultratrace thrombin by free-label aptamer-SERS method

The highly catalytic Ca-doped carbon dots (CD_Ca) were prepared by microwave procedure, that exhibit strong catalytic effect on HAuCl₄-glucose (GLC) reaction to form gold nanoparticles (AuNPs) with high SERS activity, using Victoria blue B (VBB) as a molecular probe. The SERS intensity at 1615 cm^-1 increased linearly with CD_Ca increasing, due to formation of more AuNPs nanosol substrate as indicator. When thrombin aptamer (Apt) was added in this system, Apt adsorbed on the CD_Ca surface to inhibit theirs catalytic activity, and the SERS intensity decreased. However, when thrombin (TB) was present, it can bind to Apt to form stable G-duplex of Apt-TB and free CD_Ca catalyst in the system, and the SERS signal increased linearly. Thus a free-label Apt-SERS quantitative analysis method was developed for ultratrace TB, with a linear range of 0.0058-0.115 nmol/L and a detection limit of 0.0018 nmol/L TB.

Lateral Flow Aptasensor for Simultaneous Detection of Platelet-Derived Growth Factor-BB (PDGF-BB) and Thrombin

Here we report a lateral flow aptasensor (LFA) for the simultaneous detection of platelet-derived growth factor-BB (PDGF-BB) and thrombin. Two pairs of aptamers, which are specific against PDGF-BB and thrombin, respectively, were used to prepare the LFA. Thiolated aptamers were immobilized on a gold nanoparticle (AuNP) surface and biotinylated aptamers were immobilized on the test zones of an LFA nitrocellulose membrane. The assay involved the capture of PDGF-BB and thrombin simultaneously in sandwich-type formats between the capture aptamers on the test zones of LFA and AuNP-labeled detection aptamers. AuNPs were thus captured on the test zones of the LFA and gave red bands to enable the visual detection of target proteins. Quantitative results were obtained by reading the test band intensities with a portable strip reader. By combining the highly specific molecular recognition properties of aptamers with the unique properties of lateral flow assay (low-cost, short assay time and a user-friendly format), the optimized aptasensor was capable of simultaneously detecting 1.0 nM of PDGF-BB and 1.5 nM of thrombin in association with a 10-min assay time. The biosensor was also successfully applied to detect PDGF-BB and thrombin in spiked human serum samples. The LFA shows great promise for the development of aptamer-based lateral flow strip biosensors for point-of-care or for the in-field detection of disease-related protein biomarkers.

An aptamer and functionalized nanoparticle-based strip biosensor for on-site detection of kanamycin in food samples

A lateral flow strip biosensor for fast, sensitive, low-cost and on-site detection of kanamycin was developed by using kanamycin-specific aptamer-modified gold nanoparticles (AuNPs-apt) as a probe and oligonucleotide DNA1-modified silver nanoparticles (AgNPs-DNA1) as a signal amplification element. Through the complementary sequences of DNA1 and the aptamer, the AgNP-DNA1-apt-AuNPs complex can be formed and further captured on the test zone of the strip, where a capture probe DNA2 complementary to the 3'-terminal of DNA1 was immobilized. In the presence of kanamycin, it can competitively bind to the aptamer, and then inhibit the formation of the complex and the accumulation of AuNPs on the test zone. AuNPs-apt can finally be captured on the control zone via the specific binding between biotin and streptavidin. The assay avoids multiple incubation and washing steps and can be completed within 10 min. By observing the color change of the test zone, a qualitative detection for kanamycin can be achieved by the naked eye, with the visual limit of 35 nM. Meanwhile, a linear detection range of 1-30 nM with a low detection limit of 0.0778 nM for quantitative analysis can be achieved by using a scanning reader. The lateral flow strip biosensor exhibited high specificity and stability. Moreover, it was applied to detect kanamycin in various food samples, indicating its great potential in field testing.

Applying strand displacement amplification to quantum dots-based fluorescent lateral flow assay strips for HIV-DNA detection

Up to now, the colloidal gold labeling immunochromatographic test strip is a mature and applicable technology. However, different from the conventional gold nanoparticle, quantum dot (QD) possesses larger specific surface area and better biocompatibility. So, as a novel nanomaterial, QD is capable of assembling more biomolecule which could enhance the sensitivity and accuracy of strips by rationality. Besides, strand displacement amplification was drawn into our test strips in this paper, this assumption made HIV-DNA recycling many times and converting it to plentiful QD-dsDNA (double-stranded deoxyribonucleic acid), where after these nano-structures would be captured by test zone. Meanwhile, the suggested scheme eliminated the hook effect owing to the target drop out of the incorporation on test zone, and any nucleotide sequence or substance which has aptamers can work as the target, such as carcinoembryonic antigen or mycotoxin. This assay realized the detection limit of as low as 0.76 pM (S/N = 3) and the detection range of 1 pM to 10 nM. In the end, we made use of this fluorescent lateral flow assay strips with great reproducibility for detecting HIV-DNA in human serum, that attested this method could be applied to practical application prospectively.

The aptamer-thrombin-aptamer sandwich complex-bridged gold nanoparticle oligomers for high-precision profiling of thrombin by dark field microscopy

We present a simple and efficient colorimetric assay strategy for ultrasensitive visual detection of human α-thrombin, which is essentially based on the formation of the DNA1-thrombin-DNA2 sandwich complex-bridged gold nanoparticle (Au NP) oligomers. Unlike the traditional colorimetric sensing strategies which induced the nanoparticle aggregates with uncontrolled aggregate size. In this work, the DNA1with rich G bases was firstly conjugated on the surfaces of Au NPs fixed on the hexadecyl trimethylammonium bromide (CTAB)-coated glass slide, and thrombin was captured by the DNA1. Then, the other DNA2 with rich G bases interacted with the former DNA1-thrombin complex and formed a DNA1-thrombin-DNA2 sandwich complex. The subsequently added Au NPs can be bound to the Au NP-DNA1-thrombin-DNA2 via Au-S bond to trigger the formation of Au NP oligomers, an apparent color change of the single Au NPs from green to yellow and red was observed under dark field microscopy. By measuring the intensity change of the yellow and red Au NPs, the concentration of target thrombin could be accurately quantified. As a proof of concept experiment, the formation of Au NP oligomers resulted in significantly improved sensitivity (10 fM of limit of detection and 20 fM of limit of quantity) and wider linear dynamic range of thrombin detection (20 fM-20 nM), the relative standard deviation (RSD) was less than 5.73% (n = 5). In addition, in order to validate the potential application in clinical diagnosis, the content of thrombin in a human serum samples was also quantified.

A Lateral Flow Strip Based Aptasensor for Detection of Ochratoxin A in Corn Samples

Ochratoxin A (OTA) is a mycotoxin identified as a contaminant in grains and wine throughout the world, and convenient, rapid and sensitive detection methods for OTA have been a long-felt need for food safety monitoring. Herein, we presented a new competitive format based lateral flow strip fluorescent aptasensor for one-step determination of OTA in corn samples. Briefly, biotin-cDNA was immobilized on the surface of a nitrocellulose filter on the test line. Without OTA, Cy5-labeled aptamer combined with complementary strands formed a stable double helix. In the presence of OTA, however, the Cy5-aptamer/OTA complexes were generated, and therefore less free aptamer was captured in the test zone, leading to an obvious decrease in fluorescent signals on the test line. The test strip showed an excellent linear relationship in the range from 1 ng·mL⁻¹ to 1000 ng·mL⁻¹ with the LOD of 0.40 ng·mL⁻¹, IC₁₅ value of 3.46 ng·mL⁻¹ and recoveries from 96.4% to 104.67% in spiked corn samples. Thus, the strip sensor developed in this study is an acceptable alternative for rapid detection of the OTA level in grain samples.

Highly sensitive protein detection via covalently linked aptamer to MoS2 and exonuclease-assisted amplification strategy

Molybdenum disulfide (MoS2) has shown highly attractive superiority as a platform for sensing. However, DNA physisorption on the surface of MoS2 was susceptible to nonspecific probe displacement and false-positive signals. To solve these problems, we have developed a novel MoS2-aptamer nanosheet biosensor for detecting thrombin using a covalently linked aptamer to the MoS2 nanosheet. Ten percent Tween 80 was used to prevent thrombin from nonspecific binding and to rapidly form thiol-DNA/gold nanoparticle (AuNP) conjugates. Furthermore, an MoS2 and exonuclease coassisted signal amplification strategy was developed to improve the detection limit for thrombin. We used the hybridization of the aptamer molecules and the matched strand with a 5' terminal thiol to immobilize the aptamer molecules on the surface of AuNPs in AuNPs@MoS2 nanocomposites. Exonuclease digested the single-strand aptamer and released the thrombin, which was then detected in the next recycle. With the coassisted amplification strategy, a 6 fM detection limit was achieved, showing that this method has higher sensitivity than most reported methods for thrombin detection. The results presented in this work show that this method of covalently attaching the aptamer and using the coassisted amplification is a promising technique for the detection of protein in medical diagnostics.

Gold Nanoparticles for Diagnostics: Advances towards Points of Care

The remarkable physicochemical properties of gold nanoparticles (AuNPs) have prompted developments in the exploration of biomolecular interactions with AuNP-containing systems, in particular for biomedical applications in diagnostics. These systems show great promise in improving sensitivity, ease of operation and portability. Despite this endeavor, most platforms have yet to reach maturity and make their way into clinics or points of care (POC). Here, we present an overview of emerging and available molecular diagnostics using AuNPs for biomedical sensing that are currently being translated to the clinical setting.

Ultrasensitive paper based nucleic acid detection realized by three-dimensional DNA-AuNPs network amplification

A novel three-dimensional DNA-AuNPs network structure amplification strategy was employed to design a lateral flow biosensor by introducing streptavidin coated gold nanoparticles (Au-SA) in this paper. They act as amplification probes which aggregate numerous gold nanoparticles (AuNPs) on test line by forming a three-dimensional DNA-AuNPs network structure in the presence of target. Sensitive detection of nucleic acid with point-of-care analysis is significant for infectious agent, early diagnosis and treatment of genetic diseases. The use of these particles in rapid ultrasensitive point of care (POC) lateral flow assays lead to a linear range from 0.1pM to 250nM with a limit of detection of 0.01 pM without polymerase chain reaction (PCR). The proposed method could increase the sensitivity by 4 orders of magnitudes than traditional sandwich assays labeled with AuNPs. Furthermore, the assay owns good reproducibility and stability, which will prove practical diagnostic applications.

Visual multiple recognition of protein biomarkers based on an array of aptamer modified gold nanoparticles in biocomputing to strip biosensor logic operations

We developed a strip biosensors array based on aptamer-modified gold nanoparticles as receptors and combined the protein-aptamer binding reaction with the streptavidin-biotin interaction as well as the sandwich format. We found that a series of protein receptors obtained a distinct response pattern to each target protein. Three proteins have been well distinguished with the naked eyes and a portable reader without mutual interference, accompanying with lower limit of detection and wider linear range. A complete set of four elementary logic gates (AND, OR, INH, and NAND) and eight combinative logic gates (AND-OR; AND-INH; OR-INH; INH-NAND; AND-OR-INH; AND-INH-NAND; OR-INH-NAND; AND-OR-INH-NAND) are thoroughly realized using this array, which could eventually be applicable to the keypad-lock system with enhanced complexity in the near future. Moreover, this array shows excellent linear relationships, anti-interference capability, real human serum samples applicability, long-term storage stability and reproducibility. All indicate that this design has very good prospects for development.