Fluorescence optical microscopy serves as a cornerstone of biological research, yet significant limitations persist in instrumentation accessibility, controlled intracellular delivery of nanoparticle probes, and achievement of nanometer-scale resolution. This dissertation addresses these fundamental challenges through systematic development of cost-effective imaging platforms and engineering of ultrasmall fluorescent nanoparticles for next-generation biological applications.A modular multimodal microscope system was developed that integrates spinning disk confocal and total internal reflection fluorescence imaging capabilities. The platform achieved research-grade performance with signal-to-noise ratio improvements exceeding 2.8-fold while maintaining superior modularity and cost-effectiveness compared to commercial alternatives. This work demonstrates that high-quality multimodal fluorescence microscopy can be achieved without substantial financial barriers typically associated with advanced imaging systems. To overcome limitations in nanoparticle-mediated intracellular targeting, methylene blue surface-functionalized ultrasmall aluminosilicate nanoparticles (MB-aC'dots) were engineered for photochemical internalization applications. Systematic investigation revealed that linker chemistry significantly influences both photophysical performance and cellular behavior, with longer PEG linkers enabling more effective cytosolic delivery despite lower quantum yields. The optimized platform achieved controlled endosomal escape while demonstrating nuclear accessibility and sequential co-delivery capabilities for combination therapy approaches. Ultrasmall fluorescent core-shell silica nanoparticles (C'dots) were systematically optimized for advanced optical super-resolution microscopy applications. Single-particle analysis revealed that silica encapsulation dramatically enhances critical photophysical properties, with C'dots exhibiting up to 2.2-fold improvements in photon output and extended molecular switching behavior compared to free parent dyes. Comprehensive nanobody conjugation strategies and quantitative image analysis frameworks enabled high-quality intracellular labeling of tubulin filaments. C'dots demonstrated exceptional performance in both stochastic optical reconstruction microscopy (STORM) and minimal photon flux (MINFLUX) imaging - representing the first successful application of clinically translated nanoparticles in state-of-the-art optical super-resolution techniques. Collectively, this work establishes comprehensive methodologies for advancing fluorescence microscopy through systematic optimization of both instrumentation and fluorescent probe design.