Detecting concentration of small molecules in solution

A method for conducting a small molecule assay, comprising:

• selecting a BIO-FET having a redox mediator bound to an exposed surface of a graphene layer from a stored quantity;
• applying an enzyme with sterile phosphate buffer solution (PBS) to the redox mediator-bound graphene layer;
• agitating the BIO-FET for a time period, allowing the enzyme to fully bind at the graphene surface;
• applying a DC voltage across the first and second electrodes;
• applying a digital voltmeter between the first electrode and a metal bottom layer of the BIO-FET;
• covering the graphene layer with a solution of a subject small molecule;
• allowing a time for lactate molecules in the subject solution to fully react with the enzyme;
• and
• recording a reading of the DVM as an indication of concentration of the small molecule in the subject solution.

An apparatus for conducting a small molecule assay, comprising:

• a field-effect transistor (FET) having a first and a second electrode and a metal bottom layer;
• a layer of graphene deposited on an upper surface of the FET between and in contact with the first and the second electrodes;
• a redox mediator bound to sites on the graphene layer;
• an enzyme bound to the redox mediator on the graphene layer;
• a DC power supply adapted to connect across the first and the second electrodes;
• and
• a digital voltmeter adapted to connect across the first electrode and the metal bottom layer of the BIO-FET;
• wherein a sample solution containing an unknow concentration of the small molecule applied over the graphene surface causes molecules in the sample to interact with the enzyme, causing a DC voltage to appear across the first electrode and the metal bottom layer, measurable by the DVM as an indication of concentration of the small molecule in the sample solution.

A kit for determining concentration of small molecules in a subject sample, comprising:

• a biological field-effect transistor (BIO-FET) having first and second electrodes, a metal bottom layer, a layer of graphene deposited on an upper surface of the FET between and in contact with the first and the second electrodes and a redox mediator on the graphene layer;
• a battery enabled DC power supply adapted to produce a DC voltage, the DC power supply having a first conductor ending in a first attachment interface, and a second conductor ending in a second attachment interface;
• a digital voltmeter having a display, a first cable with a first contact mechanism adapted to mate with a second contact mechanism at the first electrode, and a second cable with a third contact mechanism adapted to mate with a fourth contact mechanism at the metal bottom layer;
• a packet of dry enzyme powder;
• a capped container of phosphate buffer solution (PBS) mixed with DI water;
• a capped container of sterile phosphate buffer solution (PBS);
• and
• a plastic or glass pipette.