Here we describe an ultra-fast (< 1 min) method for coating electrochemical (EC) sensors with an anti-fouling nanocomposite layer that can be stored at room temperature for months, which provides unprecedented sensitivity and selectivity for diagnostic applications. We leveraged this method to develop a multiplexed diagnostic platform for detection of biomarkers that could potentially be used to triage patients with myocardial infarction and traumatic brain injury using only 15 microliters of blood. Single-digit pg/mL sensitivity was obtained within minutes for all the biomarkers tested in unprocessed human plasma samples and whole blood, which is much faster and at least 50 times more sensitive than traditional ELISA methods, and the signal was stable enough to be measured after one week of storage. The multiplexed EC sensor platform was validated by analyzing 22 patient samples, which demonstrated excellent correlation with reported clinical values.