The present invention relates to devices and methods of use thereof for making semiderivative voltammetric and chronoamperometric measurements of chemicals, e.g. neurotransmitters, precursors, and metabolites, in vitro, in vivo, or in situ. The invention relates to methods of diagnosing and/or treating a subject as having or being at risk of developing a disease or condition that is associated with abnormal levels of one or more neurotransmitters including, inter alia, epilepsy, diseases of the basal ganglia, athetoid, dystonic diseases, neoplasms, Parkinson's disease, brain injuries, spinal cord injuries, and cancer. The invention provides methods of differentiating white matter from grey matter using microvoltammetry. In some embodiments, regions of the brain to be resected or targeted for pharmaceutical therapy are identified using Broderick probes. The invention further provides methods of measuring the neurotoxicity of a material by comparing Broderick probe microvoltammograms of a neural tissue in the presence and absence of the material.