Electrochemical aptamer-based nanobiosensors for diagnosing Alzheimer's disease: A review

Design of an electrochemical aptasensor in the presence of an array of gold nanostructure and a GO-MWCNTs nanocomposite: application in diagnosis of Alzheimer's disease

Alzheimer's disease (AD) is considered one of the main progressive chronic diseases in elderly individuals. Early diagnosis using related biomarkers, specifically beta-amyloid peptide (Aβ), allows finding expected treatment routes. Here, we developed an electrochemical aptasensing platform for AD by employing a glassy carbon electrode (GCE) modified with a layer of jagged gold (JG) nanostructure (diameter: 60-185 nm) and graphene oxide-carboxylic acid functionalized multiwalled carbon nanotubes (GO-c-MWCNTs) nanocomposite. These surface modifications acted as the signal amplifier and provided an optimum nano-interface substrate for immobilizing aptamer strands. The measurements of Aβ were performed via differential pulse voltammetry (DPV), and the aptasensor detected the analyte in a linear range from 0.1 pg mL-1 to 1 ng mL-1, with an estimated limit of detection (LOD) of about 0.088 pg mL-1 (S/N = 3). The aptasensor showed sufficient stability (11 days), reversibility (three times), and reproducibility (five times re-fabrication with relative standard deviation (RSD): 1.27). The potential interfering agents showed negligible impact on the sensing performance. Finally, the application of the aptasensor was evaluated in the presence of 10 serum samples, and the recovery values were from 93 to 110.1%.

Sensitive detection of SARS-CoV-2 spike protein based on electrochemical impedance spectroscopy of Fe3O4@SiO2–Au/GCE biosensor

Highly contagious COVID-19 disease is caused by a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which poses a serious threat to global public health. Therefore, the development of a fast and reliable method for the detection of SARS-CoV-2 is an urgent research need. The Fe3O4@SiO2–Au is enriched with a variety of functional groups, which can be used to fabricate a sensitive electrochemical biosensor by biofunctionalization with angiotensin-converting enzyme 2 (ACE2). Accordingly, we developed a novel electrochemical sensor by chemically modifying a glassy carbon electrode (GCE) with Fe3O4@SiO2–Au nanocomposites (hereafter Fe3O4@SiO2–Au/GCE) for the rapid detection of S-protein spiked SARS-CoV-2 by electrochemical impedance spectroscopy (EIS). The new electrochemical sensor has a low limit detection (viz., 4.78 pg/mL) and a wide linear dynamic range (viz., 0.1 ng/mL to 10 μg/mL) for detecting the EIS response signal of S-protein. The robust Fe3O4@SiO2–Au/GCE biosensor has high selectivity, stability, and reproducibility for the detection of S-protein with good recovery of saliva samples.

Electrochemical Immunosensors Developed for Amyloid-Beta and Tau Proteins, Leading Biomarkers of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurological disease and a serious cause of dementia, which constitutes a threat to human health. The clinical evidence has found that extracellular amyloid-beta peptides (Aβ), phosphorylated tau (p-tau), and intracellular tau proteins, which are derived from the amyloid precursor protein (APP), are the leading biomarkers for accurate and early diagnosis of AD due to their central role in disease pathology, their correlation with disease progression, their diagnostic value, and their implications for therapeutic interventions. Their detection and monitoring contribute significantly to understanding AD and advancing clinical care. Available diagnostic techniques, including magnetic resonance imaging (MRI) and positron emission tomography (PET), are mainly used to validate AD diagnosis. However, these methods are expensive, yield results that are difficult to interpret, and have common side effects such as headaches, nausea, and vomiting. Therefore, researchers have focused on developing cost-effective, portable, and point-of-care alternative diagnostic devices to detect specific biomarkers in cerebrospinal fluid (CSF) and other biofluids. In this review, we summarized the recent progress in developing electrochemical immunosensors for detecting AD biomarkers (Aβ and p-tau protein) and their subtypes (AβO, Aβ_(1-40), Aβ_(1-42), t-tau, cleaved-tau (c-tau), p-tau₁₈₁, p-tau₂₃₁, p-tau₃₈₁, and p-tau₄₄₁). We also evaluated the key characteristics and electrochemical performance of developed immunosensing platforms, including signal interfaces, nanomaterials or other signal amplifiers, biofunctionalization methods, and even primary electrochemical sensing performances (i.e., sensitivity, linear detection range, the limit of detection (LOD), and clinical application).

Evaluation of aptamer and molecularly imprinted polymers as a first hybrid sensor for leptin detection at femtogram levels

Selective and sensitive determination of macromolecules maintains its importance in diagnosing and determining diseases to protect human health. In this study, a hybrid sensor designed with dual recognition elements consisting of both aptamers (Apt) and molecularly imprinted polymers (MIPs) was carried out for the ultra-sensitive determination of Leptin. Firstly, the screen-printed electrode (SPE) surface was coated with platinum nanospheres (Pt NSs) and gold nanoparticles (Au NPs) to provide immobilization of the Apt[Leptin] complex on the surface. In the next step, the formed polymer layer around the complex using the electropolymerization of orthophenilendiamine (oPD) kept the Apt molecules on the surface more effectively. As expected, a synergistic effect occurred between the formed MIP cavities by removing Leptin from the surface and the embedded Apt molecules to fabricate a hybrid sensor. Under optimal conditions, responses in differential pulse voltammetry (DPV) currents showed a linear response over a wide concentration range from 1.0 fg/mL to 10.0 pg/mL with a limit of detection (LOD) of 0.31 fg/mL for Leptin detection. Moreover, the effectiveness of the hybrid sensor was assessed using real samples, such as human serum and plasma samples, and satisfactory recovery findings (106.2-109.0%) were found.

Sandwich-like electrochemical aptasensing of heat shock protein 70 kDa (HSP70): Application in diagnosis/prognosis of coronavirus disease 2019 (COVID-19)

In this research, by using aptamer-conjugated gold nanoparticles (aptamer-AuNPs) and a modified glassy carbon electrode (GCE) with reduced graphene oxide (rGO) and Acropora-like gold (ALG) nanostructure, a sandwich-like system provided for sensitive detection of heat shock protein 70 kDa (HSP70), which applied as a functional biomarker in diagnosis/prognosis of COVID-19. Initially, the surface of the GCE was improved with rGO and ALG nanostructures, respectively. Then, an aptamer sequence as the first part of the bioreceptor was covalently bound on the surface of the GCE/rGO/ALG nanostructures. After adding the analyte, the second part of the bioreceptor (aptamer-AuNPs) was immobilized on the electrode surface to improve the diagnostic performance. The designed aptasensor detected HSP70 in a wide linear range, from 5 pg mL^-1 to 75 ng mL^-1, with a limit of detection (LOD) of ∼2 pg mL^-1. The aptasensor was stable for 3 weeks and applicable in detecting 40 real plasma samples of COVID-19 patients. The diagnostic sensitivity and specificity were 90% and 85%, respectively, compared with the reverse transcription-polymerase chain reaction (RT-PCR) method.

Recent Advances in Electrochemical Aptasensors for Detection of Biomarkers

The early diagnosis of diseases is of great importance for the effective treatment of patients. Biomarkers are one of the most promising medical approaches in the diagnosis of diseases and their progress and facilitate reaching this goal. Among the many methods developed in the detection of biomarkers, aptamer-based biosensors (aptasensors) have shown great promise. Aptamers are promising diagnostic molecules with high sensitivity and selectivity, low-cost synthesis, easy modification, low toxicity, and high stability. Electrochemical aptasensors with high sensitivity and accuracy have attracted considerable attention in the field of biomarker detection. In this review, we will summarize recent advances in biomarker detection using electrochemical aptasensors. The principles of detection, sensitivity, selectivity, and other important factors in aptasensor performance are investigated. Finally, advantages and challenges of the developed aptasensors are discussed.