The present invention is directed, in certain embodiments, to improved, small scale systems and methods able to selectively treat parts of a single cell, including, in certain embodiments, portions of a main body portion of a single cell, and able, in certain embodiments, to establish long-term gradients of active substances within subcellular regions of a single cell. The present invention provides, in some embodiments, techniques for selectively contacting a portion of the surface of a biological cell with a fluid or fluid component carrying a particular potential for a biophysical or biochemical interaction with the cell, and simultaneously contacting a different portion of the surface of the cell with another fluid or fluid component having a different potential for the biophysical or biochemical interaction with the cell.