Studies in the electrochemistry of single atoms, molecules, and nanoparticles

Analytical chemistry is entering an exciting era where instead of measuring over ensemble quantities of analyte species, single analyte species can be counted and studied one at a time. Intrinsic in these experiments are extremely low limits of quantitation (sub-picomolar) and, in principle, an analytical limit of detection of one. These studies also offer methods to probe the chemical and physical properties of single analyte species, which may be vastly different than properties measured over ensembles. The work in this dissertation presents several ultrasensitive methods using electrochemistry to selectively detect and study the chemical and physical properties of single entities, namely single isolated clusters, molecules, and nanoparticles. In these experiments, sub-picomolar concentrations are used to control mass transfer of analyte species to the micro or nanoelectrode such that stochastic collisions can be observed. Chapter 1 gives an introduction to stochastic electrochemical processes relevant to this dissertation. Chapter 2 investigates the collisions of single emulsion droplets (r ~ 300 nm) and their applications to bulk coulometry, electrogenerated chemiluminescence, the interface between two immiscible electrolyte solutions, and differentiation of cancerous T cells (radius ~ 3-12 μm) from healthy cells. Chapter 3 extends the stochastic study of biological species by investigating methods to selectively detect single murine cytomegalovirus particles (radius ~ 100 nm) in the urine of infected mice. The detection of single proteins (radius ~ 2-8 nm) and DNA molecules is also described. Chapter 4 pushes the limits of detection toward single ions using electrocatalytic amplification. Calibration curves obtained displayed one of the lowest limits of quantitation in analytical chemistry (femtomolar, 10⁻¹⁵ M) and the highest sensitivity for any electrochemical technique to date. The feasibility of fabricating a catalyst on an atom-by-atom basis was also explored. Platinum was electrodeposited onto carbon nanoelectrodes from femtomolar solutions of hexachloroplatinic acid, and voltammograms on the nanodeposits were attainedChemistr