Organic and inorganic nanoparticles show great potential for cancer diagnosis and treatment. Because gastric cancer (GC) represents the second most deadly type of neoplasia worldwide, continued research efforts by scientists and clinicians are essential to improve diagnosis and treatment. This paper reviews significant findings in the area of nanoparticles (organic and inorganic origin) that may aid in prevention and diagnosis of GC. This review focuses in the first section on H. pylori and the connection to GC, highlighting nanoformulations designed to control bacterial growth. The second section evaluates the potential of different imaging techniques (especially using inorganic nanoparticles) in the detection of GC, and the third section summarizes how nanotechnology may be employed in the analytical detection of GC biomarkers (metallic plasmons, electrochemical biosensors and colorimetric sensors). We foresee that the prevention and diagnosis of GC will require the development of complex collaborative studies. Additionally, scientists also need to be tightly connected to industry in order to facilitate upscaling and rapid transfer of promising products to the clinic.