Claudia Do Amaral Razzino ^1,2 Livia Flório Sgobbi ³ Juliana Cancino-Bernardi ^4* Angelica Maria Mazuera Zapata ² Clara Cardoso Costa ⁴ Valtencir Zucolotto ² Lucia Vieira ¹ Anderson Oliveira Lobo ⁵

• ¹ Universidade do Vale do Paraíba (UNIVAP), São José dos Campos, São Paulo, Brazil
• ² Institute of Physics of São Carlos, University of Sao Paulo, São Carlos, São Paulo, Brazil
• ³ Instituto de Química, Universidade Federal de Goiás, Goiania, Goias, Brazil
• ⁴ Department of Chemistry, Faculty of Philosophy, Sciences and Languages ​​of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil
• ⁵ Federal University of Piauí, Teresina, Piauí, Brazil

Alzheimer's disease is the most prevalent form of dementia and is primarily characterized by the accumulation of β-amyloid and phosphorylated tau proteins in the brain, along with the degeneration of nerve cells, which leads to impairment of various cognitive functions. A significant biomarker of Alzheimer's disease is the decreased level of soluble β-amyloid peptide (1-42) (Aβ1-42) in cerebrospinal fluid (CSF), as pathology progresses when CSF-Aβ1-42 levels drop below 192 pg mL -1 . In this study, we developed an amperometric immunosensor based on magnetic beads as the platform for constructing the immunosensor. Monoclonal antibodies are immobilized on the MBs, enabling selective detection of Aβ1-42. The detection antibody is conjugated with the enzyme horseradish peroxidase, which, in the presence of H2O2 and hydroquinone, catalyzes the decomposition of H2O2 and the oxidation of hydroquinone to p-quinone, generating an electric current measured at a potential of -200 mV (vs. the Ag pseudo-reference electrode) using screen-printed carbon electrodes. The amperometric sandwich-type immunosensor demonstrates a linear response in the concentration range of 10 to 10,000 pg mL -1 , with a detection limit of 7.4 pg mL -1 , exhibiting excellent selectivity against the assessed interferents.