Liquid metals (LMs) are a class of metals and their alloys which have low melting points near or below room temperature, and they are mainly composed of post-transition elements. The low melting points of LMs make them easily stay in a liquid state and readily be broken into tens or hundreds of nanometers, which are called LM nanoparticles (LMNPs). In this thesis, the author investigates LMNPs for three exciting applications of creating conductive polymer-LMNPs compositions and explores the potential utilization of LMNPs in biological applications. In the first phase of this research, the author develops nanocomposites of Ga-based LMNPs (EGaIn NPs) with conductive polymer polyaniline (PANI). This work reports a method of growing PANI nanofibers on the EGaIn NPs by firstly providing initial functionalization sites at the interfaces for the formation of PANI nanofibrous network. The nanocomposites provide synergistic effects of PANI nanofibers and EGaIn NPs for the applications of environmental sensing and molecular separation. In the second phase of the research, the author focused on the exploration of LMNPs for their anti-inflammatory applications. Considering that Ga ions (Ga3+), have been historically utilized as anti-inflammatory agents by interfering with the Fe homeostasis of immune cells. The study presents the anti-inflammatory effects of Ga by delivering Ga nanoparticles (Ga NPs) into lipopolysaccharide-induced macrophages. The Ga NPs show a selective anti-inflammatory effect by modulating nitric oxide production without disturbing other pro-inflammatory mediators. This work reveals the different anti-inflammatory effects between Ga NPs and Ga3+ come from their different endocytic pathways: transferrin receptor independent and dependent endocytosis for Ga NPs and Ga3+, respectively. In the final phase, the author studies the interactions between LMNPs and macrophages at a light microscopic level. The mechanistic responses of macrophages to LMNPs with different densities were observed, in comparison to some other commonly studied nanoparticles. This work discovers the mobility of macrophages is very much density-dependent. This thesis comprehensively studies the interactions between LMNPs and polymeric and biological systems, at both molecular and microscopic levels, which provides a basis and road map for utilizing LMNPs in various fields such as electronics and biomedical engineering.