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Brain-machine interfaces (BMIs), also known as brain-computer interfaces (BCIs), have emerged as a highly interdisciplinary field, bridging materials science and engineering, electrical engineering, and biology. These systems enable direct communication between the brain and external devices, offering transformative potential in neural recording, neural stimulation, sensing, and monitoring of critical physiological parameters, paving the way for improved diagnosis and therapeutic interventions. However, current clinical gold standards often rely on highly invasive procedures, including craniotomies and the surgical implantation of electrodes or probes. This dissertation focuses on the development and optimization of advanced, minimally invasive micro- and nanoscale BMIs for neural interfacing applications. The overarching goal is to improve the functionality, biocompatibility, and long-term reliability of BMI systems for applications in neural recording, sensing, stimulation, and treatment. In response to these challenges, implantable BMIs have been developed as less invasive alternatives for long-term neural interfacing. The first project presents the design of an ultra-sensitive, wireless capacitive pressure sensor for real-time intracranial pressure monitoring. By incorporating zinc oxide nanoparticles into styrene–ethylene–butylene–styrene dielectric layers, the sensor achieved a 4.3-fold improvement in sensitivity compared to sensors using pure SEBS. The second and third projects focused on the long-term performance of implantable neural interfaces through developing enhanced encapsulation strategies. In the second project, optimized pre- and post-deposition treatments of parylene C enhanced its adhesion, mechanical, and chemical stability. The third project introduced a bilayer encapsulation system for implantable optoelectronics that maintains optical transparency while ensuring protection for chronic use. The final project introduced a novel approach for wireless, battery-free photothermal neuromodulation system using urchin-shaped gold nanoparticles as efficient photothermal nanotransducers for deep brain stimulation. Integrated with a developed optoelectronic implant, this system enabled targeted neuromodulation in freely behaving mice. Ex vivo and in vivo behavioral studies confirmed effective localized hyperthermia and neural stimulation. Collectively, this work contributes to the advancement of minimally invasive, long-term BMI technologies with significant implications for clinical translation and neuroscience research.