The role of emotion and affect in science communication is a little studied phenomenon,however emotion and affect are increasingly understood as material influences on how publics relate to science and technology. Though they are recognized as being involved in shaping public perceptions of science, it is not clear what role emotion and affect play in forming what gets communicated about science before publics even appear to engage with what has been communicated. In this PhD thesis, I study how experts who communicate publicly about the science of synthetic biology accept, resist, and transform their roles as communicating experts that are offered to them by the design of a public engagement event. I constructively analyse how they inhabit these roles using Felt and Fochler’s concept of “machineries for making publics” (2010), which I interpret and operationalize as “machineries for making communicating experts.” My data consists of participant interviews, process journals, and audio diaries created in this practice-based research, wherein I produced an interactive online digital audio archive about synthetic biology called Aurator (www.aurator.org). I examine the data for key patterns pertaining to ethics, performativity, authenticity and duration as they connect to the function of emotion and affect in science communication. I conclude that the science communication that gets produced in a public engagement project is directly shaped by the emotions and affects that emerge throughout the engagement event (those of communicating experts as well as those of the engagement event producer). My findings show that affect and emotion are intractable elements of how public engagement events operate, even before publics appear, and therefore are fundamental to how science communication gets made. I argue that this calls upon science engagement practitioners to apply a special ethics of care, which I call caring for science communication, in their work. In order to care for science communication, practitioners must appreciate the performative and material nature of science communication, and be able to make compromises between multiple emergent requirements for care at every step of the way as science engagement events unfold.