Determination of the platelet-derived growth factor BB by a competitive thrombin-linked aptamer-based Fluorometric assay

Aptamer-based sensing of breast cancer biomarkers: a comprehensive review of analytical figures of merit

INTRODUCTION

Accurate determination of the aberrantly expressed biomarkers such as human epidermal growth factor receptor 2 (HER2), carcinoembryonic antigen (CEA), platelet-derived growth factor (PDGF), mucin 1 (MUC1), and vascular endothelial growth factor VEGF₁₆₅ have played an essential role in the clinical management of the breast cancer. Assessment of these cancer-specific biomarkers has conventionally relied on time-taking methods like the enzyme-linked immunosorbent assay and immunohistochemistry. However, recent development in the aptamer-based diagnostics has allowed developing tools that may substitute the conventional means of biomarker assessment in breast cancer. Adopting the aptamer-based diagnostic tools (aptasensors) to clinical practices will depend on their analytical performance on clinical samples.

AREAS COVERED

In this review, we provide an overview of the analytical merits of HER2, CEA, PDGF, MUC1, and VEGF₁₆₅ aptasensors. Scopus and Pubmed databases were searched for studies reporting aptasensor development for the listed breast cancer biomarkers in the past one decade. Linearity, detection limit, and response time are emphasized.

EXPERT OPINION

In our opinion, aptasensors have proven to be on a par with the antibody-based methods for detection of various breast cancer biomarkers. Though robust validation of the aptasensors on significant sample size is required, their ability to detect pathophysiological range of biomarkers suggest the possibility of future clinical adoption.

Affinity binding-mediated fluorometric protein assay based on the use of target-triggered DNA assembling probes and aptamers labelled with upconversion nanoparticles: application to the determination of platelet derived growth factor-BB

The target-triggered DNA assembling probe is presented for highly selective protein detection. Target-triggered DNA assembling is used in an amplification strategy based on affinity binding for identification and determination of proteins in general. Specifically, it was applied to the platelet derived growth factor-BB (PDGF-BB). A hairpin DNA (H-DNA) probe was designed containing (a) an aptamer domain for protein recognition and (b) a blocked DNAzyme domain for DNAzyme cleavage. An assistant DNA (A-DNA) probe containing aptamer and complementary domains was also employed to recognize protein and to induce DNA assembly. Once H-DNA and A-DNA recognize the same protein, H-DNA and A-DNA are in close proximity to each other. This induces DNA assembling for protein-triggered complex (Protein-Complex) with free DNAzyme domains. The free DNAzymes trigger the circular cleavage of molecular beacons for amplified signals. The assay is performed by fluorometry at an excitation wavelength of 980 nm and by collecting fluorescence at 545 nm. The platelet derived growth factor-BB (PDGF-BB) was accurately identified and selectively determined by this assay with a 22 pM detection limit (using the 3σ criterion). The responses for PDGF-BB is nearly 6-fold higher than for PDGF-AB, and 16-fold higher than PDGF-AA. This upconversion assay avoids any interference by the autofluorescence of biological fluids. Graphical abstractSchematic representation of the principle of the target-triggered DNA assembling probes mediated amplification strategy based on affinity binding for PDGF-BB. The UCNP probe is used for the quantitation of PDGF-BB with high selectivity.

A sensitive thrombin-linked sandwich immunoassay for protein targets using high affinity phosphorodithioate modified aptamer for thrombin labeling

Thrombin and its aptamers have been well studied and widely used as models in aptamer based assays and sensors. Here we reported a thrombin-linked sandwich immunoassay for proteins to demonstrate new applications of thrombin and the aptamers, converting protein detection to analysis of thrombin label. In this assay, target protein was sandwiched by the capture antibody on a microplate and the biotinylated detection antibody. Thrombin bound to one biotinylated aptamer, and then the thrombin-labeled aptamer was attached on the sandwich complex through streptavidin-biotin interaction by using streptavidin as a linker. Thrombin catalyzed cleavage of fluorogenic peptide substrates, generating fluorescence signals for target detection. Among a few different anti-thrombin aptamers, the use of one nuclease resistant RNA aptamer having phosphorodithioate (PS2) modification on a specific backbone position enabled higher assay sensitivity due to its much higher affinity. This thrombin-linked sandwich immunoassay allowed detection of prostate-specific antigen (PSA) at 2 pM, an important protein related cancer disease, with high sensitivity and specificity. The strategy was general, and also enabled sensitive detection of botulinum neurotoxin type A (BoNTA) light chain, one toxin protein causing risk to human health. This assay combines advantages of antibody recognition, aptamer affinity labeling, high affinity of aptamers, and enzyme activity of thrombin. Labeling thrombin on the immunosandwich complex through simple affinity binding overcomes limitations of covalent conjugating enzyme on antibody in conventional immunoassay. This assay is promising in applications for protein detection.

A competitive thrombin-linked aptamer assay for small molecule: aflatoxin B1

We described a competitive thrombin-linked aptamer assay for small molecule, using aflatoxin B₁ (AFB₁) as a model, taking advantage of aptamer affinity binding and enzymatic activity of thrombin. We designed a dual functional DNA probe that contained the aptamer sequence for thrombin and the aptamer sequence for AFB₁. Thrombin was labeled on the DNA probe by affinity binding between thrombin and anti-thrombin aptamer. This thrombin-labeled DNA probe was attached on AFB₁-bovine serum albumin conjugate (BSA-AFB₁) coated on a microplate through the affinity interaction between AFB₁ and anti-AFB₁ aptamer. The thrombin attached on the microplate catalyzed the cleavage of peptide substrate into detectable product, generating signal for detection. In the presence of AFB₁, free AFB₁ competed with BSA-AFB₁ in the binding to the limited amount of DNA probe, leading to signal decrease. Detection of AFB₁ was achieved by measuring the signal change. Under optimized conditions, AFB₁ was successfully detected in the range from 0.5 nM to 1 μM when fluorogenic peptide substrate of thrombin and fluorescence analysis were applied. The use of chromogenic peptide substrate in the assay allowed the detection of AFB₁ ranging from 0.5 to 125 nM by simple absorbance analysis. The thrombin-linked aptamer assay showed good selectivity towards AFB₁, and enabled the detection of AFB₁ spiked in diluted beer and corn flour. This TLAA strategy extends the analytical application of thrombin and aptamers in detection of small molecules. Graphical abstract.

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.

Electrochemiluminescent aptasensor for thrombin using nitrogen-doped graphene quantum dots

An electrochemiluminescent (ECL) aptamer based method is described for the determination of thrombin. Three-dimensional nitrogen-doped graphene oxide (3D-NGO) was placed on a glassy carbon electrode (GCE) to provide an electrode surface that displays excellent electrical conductivity and acts as a strong emitter of ECL. The modified electrode was further coated with chitosan via electrodeposition. Finally, the amino-modified aptamer was immobilized on the modified GCE. The interaction between thrombin and aptamer results in a decrease in ECL. The assay has a linear response in the 1 fM to 1 nM thrombin concentration range and a 0.25 fM lower detection limit (at an S/N ratio of 3). The method was applied to the determination of thrombin in spiked human plasma samples, and recoveries ranged between 94 and 105% (with RSDs of <3.6%). The calibration plot was recorded at potential and wavelength of fluorescence emission (wavelength: 445 nm; potential: 0 to -2 V). Graphical abstract A bare glassy carbon electrode (GCE) does not display electrochemiluminescence (ECL). If, however, nitrogen-doped graphene quantum dots, chitosan, and three-dimensional nitrogen-doped graphene oxide (NGQD-chitosan/3D-NGO) are electrodeposited on the GCE, strong ECL can be observed. The ECL intensity decreased after aptamer and bovine serum albumin (BSA) were dropped onto the electrode (curve a). However, the ECL further decreases after addition of thrombin (TB; curve b).

A dual-channel homogeneous aptasensor combining colorimetric with electrochemical strategy for thrombin

In this protocol, a dual-channel homogeneous aptasenor was proposed for protein molecule determination, employing thrombin as target analyte. The colorimetric and electrochemical transducers were combined in a single analytical system for signal readout. In this dual-channel sensing strategy, the G-quadruplex sequence was released and incorporated with hemin to form DNAzyme for naked-eye colorimetric detection. Meanwhile, the hydroxyapatite nanoparticle as signal probe was combined with magnetic nanoparticles to construct sandwich-type structure for generating the electrochemical current when thrombin was present in solution. By introducing two kinds of reporter probes and transducers, this dual-channel sensor produced two different kinds of signal to improve the analytical accuracy and diversity. The results revealed that the dual-channel sensor achieved the quantatitive determination of thrombin with low limit of detection (0.40 fM) and wide range (0.1 fM to 1 nM), which offer a promise for rapid and accurate detection of biomolecule.

Recent advances on aptamer-based biosensors to detection of platelet-derived growth factor

Platelet-derived growth factor (PDGF-BB), a significant serum cytokine, is an important protein biomarker in diagnosis and recognition of cancer, which straightly rolled in proceeding of various cell transformations, including tumor growth and its development. Fibrosis, atherosclerosis are certain appalling diseases, which PDGF-BB is near to them. Generally, the expression amount of PDGF-BB increases in human life-threatening tumors serving as an indicator for tumor angiogenesis. Thus, identification and quantification of PDGF-BB in biomedical fields are particularly important. Affinity chromatography, immunohistochemical methods and enzyme-linked immunosorbent assay (ELISA), conventional methods for PDGF-BB detection, requiring high-cost and complicated instrumentation, take too much time and offer deficient sensitivity and selectivity, which restrict their usage in real applications. Hence, it is essential to design and build enhanced systems and platforms for the recognition and quantification of protein biomarkers. In the past few years, biosensors especially aptasensors have been received noticeable attention for the detection of PDGF-BB owing to their high sensitivity, selectivity, accuracy, fast response, and low cost. Since the role and importance of developing aptasensors in cancer diagnosis is undeniable. In this review, optical and electrochemical aptasensors, which have been applied by many researchers for PDGF-BB cancer biomarker detection, have been mentioned and merits and demerits of them have been explained and compared. Efforts related to design and development of aptamer-based biosensors using nanoparticles for sensitive and selective detection of PDGF-BB have been reviewed considering: Aptamer importance as recognition elements, principal, application and the recent improvements and developments of aptamer based optical and electrochemical methods. In addition, commercial biosensors and future perspectives for rapid and on-site detection of PDGF-BB have been summarized.