Lateral flow aptasensor for progesterone: Competitive target recognition and displacement of short complementary sequences

A nitrogen-doped hollow carbon nanospheres-based aptasensor for non-invasive salivary detection of progesterone

Developing an easy-to-use and non-invasive sensor for monitoring progesterone (P4) as a multi-functional hormone is highly demanded for point-of-care testing. In this study, an ultrasensitive electrochemical aptasensor is fabricated for monitoring P4 in human biofluids. The sensing interface was designed based on the porous nitrogen-doped hollow carbon spheres (N-HCSs). The N-HCSs covalently immobilized high-dense aptamer (Apt) sequences as the bioreceptor of P4. The electron transfer of the redox probe was hindered by incubating P4 on the aptasensor surface and forming the P4-Apt complexes. Meanwhile, the signaling was decreased under two wide linear dynamic ranges (LDRs) from 10 fM to 5.6 μM with a limit of detection (LOD) value of 3.33 fM. The aptasensor presented satisfactory selectivity in the presence of different off-target species with successful feasibility for P4 detection in some human urine and saliva samples. The aptasensor with high sensitivity, as an advantage for on-site and sensitive measurement of P4, can be considered a non-invasive tool for routine analysis of real-world clinical samples method.

Paper-Based Biosensors for the Detection of Nucleic Acids from Pathogens

Paper-based biosensors are microfluidic analytical devices used for the detection of biochemical substances. The unique properties of paper-based biosensors, including low cost, portability, disposability, and ease of use, make them an excellent tool for point-of-care testing. Among all analyte detection methods, nucleic acid-based pathogen detection offers versatility due to the ease of nucleic acid synthesis. In a point-of-care testing context, the combination of nucleic acid detection and a paper-based platform allows for accurate detection. This review offers an overview of contemporary paper-based biosensors for detecting nucleic acids from pathogens. The methods and limitations of implementing an integrated portable paper-based platform are discussed. The review concludes with potential directions for future research in the development of paper-based biosensors.

Carbon Dots Conjugated Antibody as an Effective FRET-Based Biosensor for Progesterone Hormone Screening

In this work, carbon dots (CDs) were synthesized by a one-step hydrothermal method using citric acid and ethylene diamine, and covalently functionalized with antibodies for the sensing of progesterone hormone. The structural and morphological analysis reveals that the synthesized CDs are of average size (diameter 8-10 nm) and the surface functionalities are confirmed by XPS, XRD and FT-IR. Further graphene oxide (GO) is used as a quencher due to the fluorescence resonance energy transfer (FRET) mechanism, whereas the presence of the analyte progesterone turns on the fluorescence because of displacement of GO from the surface of CDs effectively inhibiting FRET efficiency due to the increased distance between donor and acceptor moieties. The linear curve is obtained with different progesterone concentrations with 13.8 nM detection limits (R2 = 0.974). The proposed optical method demonstrated high selectivity performance in the presence of structurally resembling interfering compounds. The PL intensity increased linearly with the increased progesterone concentration range (10-900 nM) under the optimal experimental parameters. The developed level-free immunosensor has emerged as a potential platform for simplified progesterone analysis due to the high selectivity performance and good recovery in different samples of spiked water.

Progress in Biosensors for the Point-of-Care Diagnosis of COVID-19

Coronavirus disease 2019 (COVID-19) is a highly virulent infection that has caused a pandemic since 2019. Early diagnosis of the disease has been recognized as one of the important approaches to minimize the pathological impact and spread of infection. Point-of-care tests proved to be substantial analytical tools, and especially lateral flow immunoassays (lateral flow tests) serve the purpose. In the last few years, biosensors have gained popularity. These are simple but highly sensitive and accurate analytical devices composed from a selective molecule such as an antibody or antigen and a sensor platform. Biosensors would be an advanced alternative to current point-of-care tests for COVID-19 diagnosis and standard laboratory methods as well. Recent discoveries related to point-of-care diagnostic tests for COVID-19, the development of biosensors for specific antibodies and specific virus parts or their genetic information are reviewed.

Lateral flow assays for hormone detection

Endocrine diseases are the fifth most common cause of death and have a considerable impact on society given that they induce long-term morbidity in patients. For many decades, the measurement of hormones has been of great interest since this can be used to diagnose a plethora of pathological conditions. As a result, the endocrine testing market has experienced exponential growth. Several techniques have been utilised for the detection of hormones; however, they are expensive, laborious and require specialist training. Conversely, lateral flow assays (LFAs) are cheap (<£1) and rapid (<5 min) devices. LFAs typically rely on biochemical interactions between antibodies and antigens to produce coloured signals proportional to analyte concentrations, which can be visually inspected. Given their simplicity, LFAs are now considered the most attractive point-of-care device in medicine. However, the measurement of hormones in biofluids using LFAs faces many challenges including (i) the necessity for sensitive detection methods, (ii) the need for multiplexed devices for the confirmation of a diagnosis, and (iii) difficulties in sample preparation and pre-concentration. As such, most hormone LFAs remain in the research phase, and the few that have been commercialised require further optimisation before they can be employed for routine use. This review summarises the basic principles underlying lateral flow technology and provides an overview of recent advances, challenges, and potential solutions for the detection of hormone biomarkers via LFAs. Finally, hormone LFA kits available on the market are presented, with a look towards future developments and trends in the field.

Aptamer-Based Lateral Flow Assays: Current Trends in Clinical Diagnostic Rapid Tests

The lateral flow assay (LFA) is an extensively used paper-based platform for the rapid and on-site detection of different analytes. The method is user-friendly with no need for sophisticated operation and only includes adding sample. Generally, antibodies are employed as the biorecognition elements in the LFA. However, antibodies possess several disadvantages including poor stability, high batch-to-batch variation, long development time, high price and need for ethical approval and cold chain. Because of these limitations, aptamers screened by an in vitro process can be a good alternative to antibodies as biorecognition molecules in the LFA. In recent years, aptamer-based LFAs have been investigated for the detection of different analytes in point-of-care diagnostics. In this review, we summarize the applications of aptamer technology in LFAs in clinical diagnostic rapid tests for the detection of biomarkers, microbial analytes, hormones and antibiotics. Performance, advantages and drawbacks of the developed assays are also discussed.

Highly sensitive and selective lateral flow aptasensor for anti-coagulant dabigatran etexilate determination in blood

Dabigatran etexilate (DBG) is a new anticoagulant drug (commercially sold under the names Pradaxa® and Pradax™) that replaces Warfarin, the landmark agent for anticoagulation therapy. Inadequate administration of DBG or in the cases of massive bleeding that occurs after renal impairment, DBG therapy can carry a substantial life-threatening risks. One of the major limitations of DBG treatment is the lack of a simple and quick tool for measuring its level in blood in the case of massive bleedings or emergency operations. In this work, we have incorporated a previously isolated aptamer for DBG to develop a simple competitive lateral flow aptasensor (LFA) for the determination of DBG in buffer and blood samples. A full-length 60-mer aptamer as well as a truncated 38-mer aptamer were conjugated to gold nanoparticles (AuNPs) via thiol-Au coupling chemistry. After appropriate AuNP surface passivation steps, the aptamer's core region was hybridized with 8-mer biotinylated sequences. The conjugated particles could be capture on the test line by the interaction of the biotin molecules with a previously deposited streptavidin. Incubation of the conjugated particles with DBG causes the aptamer to undergo a conformational change that releases the 8-mer biotinylated sequences and result in the disappearance of the test line. Lysozyme protein was used to construct the control line that non-specifically interacts with the conjugated particles whether or not the target compound is present. The developed LFA achieves 20 nM detection level in buffer and blood samples, operates within the nanomolar range, and shows excellent selectivity against potential interfering molecules. The developed sensor could help assessing the levels of DBG in medical conditions that require rapid interventions.

Aptamer-based lateral flow assay on-site biosensors

The lateral flow assay (LFA) is a widely used paper-based on-site biosensor that can detect target analytes and obtain test results in several minutes. Generally, antibodies are utilized as the biorecognition molecules in the LFA. However, antibodies selected using an in vivo process not only may risk killing the animal hosts and causing errors between different batches but also their range is restricted by the refrigerated conditions used to store them. To avoid these limitations, aptamers screened by an in vitro process have been studied as biorecognition molecules in LFAs. Based on the sandwich or competitive format, the aptamer-based LFA can accomplish on-site detection of target analytes. Since aptamers have a distinctive ability to undergo conformational changes, the adsorption-desorption format has also been exploited to detect target analytes in aptamer-based LFAs. This paper reviews developments in aptamer-based LFAs in the last three years for the detection of target analytes. Three formats of aptamer-based LFAs, i.e., sandwich, competitive, and adsorption-desorption, are described in detail. Based on these formats, signal amplification strategies and multiplexed detection are discussed in order to provide an overview of aptamer-based LFAs for on-site detection of target analytes. In addition, the potential commercialization and future perspectives of aptamer-based LFAs for rapid detection of SARS-CoV-2 are given to support the COVID-19 pandemic.

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.

An electrochemical biosensing platform for progesterone hormone detection using magnetic graphene oxide

In recent times, graphene and its derivatives have turned out to be emerging nanomaterials as transducers to promote electron transport in the field of biosensing using electrochemical techniques. In electrochemical biosensing strategies, key factors such as signal amplification, stability, and sensitivity are necessary for attaining improved sensor performance. In the present work, we synthesized magnetic nanocomposites of graphene oxide and employed them as an electrode material for the loading of bio receptors. The increased surface area with high electric conductance enhanced the sensor's response. The immobilization of progesterone (PGN) antibodies on the modified electrode-sensing surface led to a hindered electron transport that decreased the current response. The developed electrochemical immunosensor assembled successfully in a stepwise process using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) studies along with the electrochemical impedance spectroscopy (EIS) analysis. The current response decreased linearly with the increased progesterone (PGN) concentration range of 0.01 pM-1000 nM with excellent detection limits of 0.15 pM (DPV) and 0.17 pM (CV) under optimal experimental conditions. The label-free electrochemical immunosensor has shown a promising platform for rapid and direct analysis of PGN due to its high sensitivity, selectivity, stability, and repeatability in water samples.

Aptasensors for Point-of-Care Detection of Small Molecules

Aptamers, a group of nucleic acids which can specifically bind to a target molecule, have drawn extensive interest over the past few decades. For analytics, aptamers represent a viable alternative to gold-standard antibodies due to their oligonucleic nature combined with advantageous properties, including higher stability in harsh environments and longer shelf-life. Indeed, over the last decade, aptamers have been used in numerous bioanalytical assays and in various point-of-care testing (POCT) platforms. The latter allows for rapid on-site testing and can be performed outside a laboratory by unskilled labor. Aptamer technology for POCT is not limited just to medical diagnostics; it can be used for a range of applications, including environmental monitoring and quality control. In this review, we critically examine the use of aptamers in POCT with an emphasis on their advantages and limitations. We also examine the recent success of aptasensor technology and how these findings pave the way for the analysis of small molecules in POCT and other health-related applications. Finally, the current major limitations of aptamers are discussed, and possible approaches for overcoming these challenges are presented.

Application of aptamers as molecular recognition elements in lateral flow assays

Owing to their ease in operation and fast turnaround time, lateral flow assays (LFAs) are increasingly being used as point-of-care diagnostic tests for variety of analytes. In a majority of these LFAs, antibodies are used as a molecular recognition element. Antibodies have a number of limitations such as high batch-to-batch variation, poor stability, long development time, difficulty in functionalization and need for ethical approval and cold chain. All these factors pose a great challenge to scale up the antibody-based tests. In recent years, the advent of aptamer technology has made a paradigm shift in the point-of-care diagnostics owing to the various advantages of aptamers over antibodies that favour their adaptability on a variety of sensing platforms including the lateral flow. In this review, we have highlighted the advantages of aptamers over antibodies, suitability of aptamers for lateral flow platforms, different types of aptamer-based LFAs and various labels for aptamer-based LFAs. We have also provided a summary of the applications of aptamer technology in LFAs for analytical applications.