Spatially Resolved Detection of Attomole Quantities of Organic Molecules Localized in Picoliter Vials Using Time-of-Flight Secondary Ion Mass Spectrometry

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Abstract
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been utilized to detect femtomole and attomole quantities of organic species from within silicon nanovials. By using high-density arrays (10 000 nanovials/cm2) it is possible to chemically characterize diverse sample sets within a single chemical image. Molecular sensitivities, for the compounds investigated, vary between 85 attomoles and 25 femtomoles, and typical acquisition times are approximately 100 ms per nanovial. These vials are fabricated using photolithography and KOH etching of Si{001} wafers to create wells, with a pyramidal cross section, ranging in size from 25 to 5625 μm2. The volume ranges from 30 femtoliters to 100 picoliters, respectively. A drawn glass microinjector and solenoid-driven dispenser are utilized to array picoliter volumes of organic compounds into individual silicon nanovials. Solution concentrations typically range from 1 × 10-2 to 1 × 10-4 M allowing femtomole and even attomole quantities of material to be dispensed into each vial.