A Simple and Cost-Effective Electrochemical Assay for Heart Failure Prognosis Using Soluble Suppression of Tumorigenicity 2‑Specific Nanobodies.

Heart failure (HF) is a major global health concern, particularly in low- and middle-income countries where it is often underdiagnosed. Prognostic testing plays a crucial role in guiding treatment and monitoring disease progression. In this study, we developed an electrochemical assay-based prognostic kit for HF detection targeting soluble suppression of tumorigenicity 2 (sST2). This biomarker offers superior prognostic value compared to traditional methods as it remains stable regardless of patient demographics, including age, sex, obesity, and renal status. To reduce production costs and complexity of the test kit, single-domain antibody fragments (nanobodies) were used in place of conventional antibodies, and an electrochemical platform was used instead of ELISA. We obtained 19 candidate nanobodies from screening a naïve, fully synthetic yeast-display nanobody (Nb) library, and four of these (Nb1, Nb2, Nb5, and Nb13) were prioritized for further study on the basis of high affinity and low polyreactivity. Of these, Nb2 and Nb5 enabled sensitive electrochemical detection of sST2 with limits of detection of 3.37 and 3.00 ng/mL, respectively, in PBS buffer. Further validation using patient serum samples with the Nb5-based platform achieved quantitative detection of sST2 across a predilution concentration range from 0.75 to 93.09 ng/mL, facilitated by sample dilution to mitigate matrix effects and surface saturation. Both nanobodies exhibited high target specificity, with no observed cross-reactivity to other HF biomarkers or serum components. This novel prognostic tool can be produced and performed at low cost, providing a new option for heart failure diagnosis and treatment planning, particularly in low- and middle-income countries, where cost is a major cause of underdiagnosis.