Microplastics, defined as particles of plastic tens of microns to millimeters in size, are becoming pervasive in the world oceans due to anthropogenic pollution (Rochman 2013). The size of microplastics is of great concern, because it results in physiological problems in a variety of marine organisms. Plastic polymers have chemical structures that allow for the absorption of persistent organic pollutants (Fernandez 2012) and obstruct digestive tracts of filter feeding organisms, leading to increased mortality (Brown 2006). The ocean has spatially diverse concentrations of surface microplastics, so attempting to identify trends in global dispersal patterns is difficult and expensive using current research techniques. Understanding the global dispersion patterns and degradation rates of microplastics will help to determine the associated human and ecosystem impacts. A novel low-cost oceanographic sensor has been designed that can determine the concentration of marine microplastics over large spatial areas. This sensor can selectively remove plastic particulates from seawater and archive them for later elemental analysis, determine microplastic concentration for 28 discrete samples based on GPS positioning, and record salinity and water temperature measurements. This sensor has been designed around the open-source Arduino platform, allowing for maximum implementation of additional sensors and systems in future prototypes. This sensor can be implemented on a mooring, drifter, or attach to an Autonomous Underwater Vehicle (AUV) to gather diverse data on the dispersion of microplastics. This sensor could drastically lower research costs associated with open ocean research cruises and greatly increase our understanding of dispersion and degradation rates in marine microplastics.