ONI, a biotechnology company democratizing the ability to observe single molecules in living cells with its desktop Nanoimager microscopy platform, today announced the closing of a $75 million Series B financing. The round was led by ARCH Venture Partners and Casdin Capital, with participation from Section 32, ARTIS Ventures, Vertical Venture Partners, Axon Ventures and private investors, including Paul Conley. Existing investors, including Oxford Science Enterprises, also participated in the round.