Shot noise sets the limit of quantification in electrochemical measurements

Detection of single molecules, particles, and rapid redox events is a challenge of electrochemical investigations and requires either an amplification strategy or significant aver-aging for the electrochemical current to exceed the noise level. We consider the minimum number of electrons required to reach the limit of quantification in these electrochemical measurements. A survey of the literature indicates that the state-of-the-art limit in current detection for different types of measurements (e.g. voltammetry, single molecule redox cycling, ion channel recordings of single molecules, metal nanoparticle collision, and phase nucleation) is independent of the nature of the measurement and increases linearly with reciprocal response time, Delta t(-1), over-5 orders of magnitude (from similar to 10 to similar to 106 s(-1)). We demonstrate that the practical limit of quantification requires cumulative measurement of similar to 2100 electrons during At and is determined by statistics of counting electrons, that is, the shot noise in the current.