Gold Nanoparticle-Decorated Catalytic Micromotor-Based Aptassay for Rapid Electrochemical Label-Free Amyloid-ß42 Oligomer Determination in Clinical Samples from Alzheimer's Patients.

Micromotor (MM) technology offers a valuable and smart on-the-move biosensing microscale approach in clinical settings where sample availability is scarce in the case of Alzheimer's disease (AD). Soluble amyloid-ß protein oligomers (AßO) (mainly AßO42) that circulate in biological fluids have been recognized as a molecular biomarker and therapeutic target of AD due to their high toxicity, and they are correlated much more strongly with AD compared to the insoluble Aß monomers. A graphene oxide (GO)-gold nanoparticles (AuNPs)/nickel (Ni)/platinum nanoparticles (PtNPs) micromotors (MMGO-AuNPs)-based electrochemical label-free aptassay is proposed for sensitive, accurate, and rapid determination of AßO42 in complex clinical samples such as brain tissue, cerebrospinal fluid (CSF), and plasma from AD patients. An approach that implies the in situ formation of AuNPs on the GO external layer of tubular MM in only one step during MM electrosynthesis was performed (MMGO-AuNPs). The AßO42 specific thiolated-aptamer (AptAßO42) was immobilized in the MMGO-AuNPs via Au-S interaction, allowing for the selective recognition of the AßO42 (MMGO-AuNPs-AptAßO42-AßO42). AuNPs were smartly used not only to covalently bind a specific thiolated-aptamer for the design of a label-free electrochemical aptassay but also to improve the final MM propulsion performance due to their catalytic activity (approximately 2.0× speed). This on-the-move bioplatform provided a fast (5 min), selective, precise (RSD < 8%), and accurate quantification of AßO42 (recoveries 94-102%) with excellent sensitivity (LOD = 0.10 pg mL-1) and wide linear range (0.5-500 pg mL-1) in ultralow volumes of the clinical sample of AD patients (5 µL), without any dilution. Remarkably, our MM-based bioplatform demonstrated the competitiveness for the determination of AßO42 in the target samples against the dot blot analysis, which requires more than 14 h to provide qualitative results only. It is also important to highlight its applicability to the potential analysis of liquid biopsies as plasma and CSF samples, improving the reliability of the diagnosis given the heterogeneity and temporal complexity of neurodegenerative diseases. The excellent results obtained demonstrate the analytical potency of our approach as a future tool for clinical/POCT (Point-of-care testing) routine scenarios.

Serum Autoantibody Biomarkers for Management of Rheumatoid Arthritis Disease.

Rheumatoid arthritis (RA) is a systemic chronic autoimmune inflammatory disease that is characterized by the destruction of bone and production of autoantibodies such as rheumatoid factor (RF) and anticitrullinated protein antibodies (ACPAs). The high prevalence of this disease and the need of affordable tools for its early detection led us to prepare the first electrochemical immunoplatform for the simultaneous determination of four RA biomarkers, the autoantibodies: RF, anti-peptidyl-arginine deiminase enzyme (anti-PAD4), anti-cyclic citrullinated peptide (anti-CCP), and anti-citrullinated vimentin (anti-MCV). Functionalized magnetic beads (MBs) were used to immobilize the specific antigens, and sandwich-type immunoassays were implemented for the amperometric detection of the four autoantibodies, using the horseradish peroxidase (HRP)/H2O2/hydroquinone (HQ) system. The immunoplatform was applied to the determination of the biomarkers in human serum of twenty-two patients diagnosed with RA and four healthy individuals, and the results were validated against ELISA tests and the certified values.

Synthesis, characterization and use of enzyme cashew gum nanoparticles for biosensing applications.

This research reports, for the first time, the immobilization of an enzyme - Rhus vernificera laccase - on cashew gum (CG) nanoparticles (NPs) and its application as a biological layer in the design and development of an electrochemical biosensor. Laccase-CG nanoparticles (LacCG-NPs) were prepared by the nanoprecipitation method and characterized by UV-Vis spectrophotometry, atomic force microscopy, scanning electron microscopy, attenuated total reflectance-Fourier-transform infrared spectroscopy, circular dichroism, cyclic voltammetry, and electrochemical impedance spectroscopy. The average size and stability of the NPs were predicted by DLS and zeta potential. The ATR-FTIR results clearly demonstrated an interaction between -NH and -OH groups to form LacCG-NPs. The average size found for LacCG-NPs was 280 ± 53 nm and a polydispersity index of 0.309 ± 0.08 indicated a good particle size distribution. The zeta potential shows a good colloidal stability. The use of a natural product to prepare the enzymatic nanoparticles, its easy synthesis and the immobilization efficiency should be highlighted. LacCG-NPs were successfully applied as a biolayer in the development of an amperometric biosensor for catechol detection. The resulting device showed a low response time (6 s), good sensitivity (7.86 µA µM-1 cm-2), wide linear range of 2.5 × 10-7-2.0 × 10-4 M, and low detection limit (50 nM).

Fast and sensitive diagnosis of autoimmune disorders through amperometric biosensing of serum anti-dsDNA autoantibodies.

This work reports the first amperometric biosensor involving the use of neutravidin-functionalized magnetic microbeads (NA-MBs) modified with a biotinylated-anti-dsDNA (b-dsDNA) as efficient magnetic microcarriers to selectively capture anti-dsDNA autoantibodies (IgG, IgA and IgM AAbs) present in the sera of patients with rheumatoid arthritis (RA). Subsequently, the attached anti-dsDNA AAbs are detected with a mixture of conventional HRP-labeled secondary antibodies (HRP-anti-human IgG/IgM/IgA mixture). The biorecognition event is monitored by amperometric transduction using the hydroquinone (HQ)/H2O2 system upon capturing the modified MBs on the surface of screen-printed carbon electrodes (SPCEs). The developed bioplatform exhibits a linear calibration plot ranging from 1 to 200 IU mL-1 with a LOD of 0.3 IU mL-1 for anti-dsDNA AAbs standards. In addition, the biosensor allows performing the determination of the anti-dsDNA AAbs levels directly in 100-times diluted serum samples from patients diagnosed with RA and in just 75 min. The obtained results are in agreement with those provided by an ELISA kit and allow discrimination between positive and negative samples.