Cardiovascular diseases are the number one cause of death worldwide. Cardiac biomarkers can provide objective and quantitative information to facilitate early diagnosis and guide treatment of cardiovascular diseases. Even though a variety of methods have been developed for cardiac biomarker detection, a point-of-care testing (POCT) for cardiac biomarkers with high sensitivity, specificity and precision is still missing. To fulfil this unmet need, novel digital biosensing methods based on optical imaging and nanomaterials are developed in this dissertation for high-sensitivity POCT of cardiac biomarkers.First, a high-sensitivity and POC-compatible optical imaging-based digital immunoassay is developed for rapid detection of low-abundance biomarkers. This technology was established on a model analyte IL-6 and can be adapted to various other protein targets. The digital immunoassay was also utilized as the reference method for evaluating the digital nanobiosensors developed afterwards. Second, a microfluidic digital nanobiosensor (MDNB) is developed for POC-compatible detection of heart failure biomarker NT-proBNP from 7 µL of whole blood. Using the MDNB, detection in a clinically relevant concentration range was achieved with a 10-minute assay time. With a high potential utility in outpatient and possibly even home settings, the MDNB could become a POC device for decentralized detection of NT-proBNP to assist heart failure patient management. Lastly, the development of a digital immunogold-linked apta-sorbent assay (DILASA) for rapid high-sensitivity detection of heart attack biomarker cardiac troponin is introduced. Reliable detection of 10 ng/L cTnT in human plasma was achieved with a 15-minute assay time using DILASA. It is expected that with further optimization and development, DILASA will be a promising candidate approach for realizing a high-sensitivity POCT of cTnT.