A nanoparticle refers to any nanoscale unit that functions as a coherent whole. Because they have significantly more surface area by weight, nanoparticles of a given substance may behave extremely differently from larger particles of the same substance. Nanoparticles have a wide range of existing and potential applications in medicine, manufacturing and electronics. Some of the many current applications include the production of low-cost solar cells and UV-protective coatings, scrubbing arsenic from water, and making chemotherapy drugs more effective. The small size of nanoparticles allow them to pass through cell membranes and potentially interact with DNA and other molecular structures. Because of this, there is concern about the untested effects of nanoparticles in medicines, cosmetics and other applications.