Category: Assay Development and Screening
Dopamine, being a neurotransmitter and a key chemical messenger, serves to signal nerve cells that initiate functions such as: movement, behavior, attention, sleep and mood. Abnormally high levels of dopamine are capable of propagating moods of anxiety, cognitive acuity, and energetic feelings. Low levels of dopamine can lead to learning disorders like ADD/ADHD, and even indicate the early signs of Parkinson’s disease, a crippling disorder which inhibits certain nerve cells ability to produce dopamine. Dopamine is found in multiple medians such as urine, blood, sweat, and salvia. In adults, dopamine is expressed in blood in a range of 0.13 nM, and expressed in urine in a range of 3139 nM. A biosensor capable of low volume point of care dopamine sensing presents a promising development to those researching any of the disorders discussed earlier.
Due to the incredibly small concentrations of dopamine, a process known as electrochemical impedance spectroscopy (EIS) was utilized. The electrode array consisted of a silver reference electrode, accompanied by gold working and counter electrodes, and were fabricated through thin film deposition onto a flexible polymer base substrate. By applying a potential to the dopamine containing solution an electrical double layer was modulated between the surface of the electrode and the dopamine containing PBS solution. The double layer modulates as dopamine molecules, which use crosslinkers to form an intermediate link between the dopamine specific antibody and the sensor, are bound onto the surface of the electrode. This produces unique changes in the impedance. Through analyzing these changes in impedance, the presence of dopamine in the solution can be discerned.
The sensor exhibited a concentration dependent impedance response with respect to logarithmically increasing concentrations of dopamine suspended in PBS. A control experiment which was conducted using a PBS solution lacking any dopamine in it exhibited a 4% impedance change. Even the smallest concentration of dopamine tested, 10-5 nM, produced an impedance change of 39%. These results lead one to believe that the impedance response observed was a direct result of the presence of dopamine binding to the constructed affinity assay, rather than the impedance being a result of non-specific factors such as physical absorption of small molecules or degradation of the assay. The sensor was only capable of detecting dopamine up to a concentration of 100 nM, thus the sensor would be able to detect dopamine in blood but not in urine. The incredibly small form factor of this sensor along with the relatively inexpensive materials from which it was constructed make this sensor a promising analytical device for detecting dopamine.
Jakob Morrow– Student, UT Dallas, Richardson, TX