Hydrogel biosensor

A method of determining the concentration of free analyte in a solution, comprising the steps of:

• providing a hydrogel having pendant charged moieties, analyte molecules, and analyte-specific binding molecules covalently immobilized therein;
• enclosing the hydrogel in a rigid structure which has at least one permeable portion available for contacting a test fluid with the hydrogel, the permeable portion constructed to permit free analyte to diffuse into the hydrogel;
• contacting the hydrogel sequentially with a series of calibration solutions having known concentrations of free analyte;
• measuring osmotic pressure in the hydrogel for each of the calibration solutions to produce a calibration curve of osmotic pressure versus analyte concentration;
• contacting the hydrogel with the test fluid, and measuring a resulting osmotic pressure;
• and
• comparing the resulting osmotic pressure with the calibration curve to determine analyte concentration of the test fluid.

A sensor for measuring the concentration of free molecules of an analyte in a fluid, comprising:

• a rigid enclosure having an open end and a closed end, the open end being covered by a semipermeable membrane;
• a diaphragm positioned within the enclosure between the semipermeable membrane and the closed end;
• a polymeric hydrogel having pendant moieties which are charged at physiological pH, the hydrogel being enclosed between the semipermeable membrane and the diaphragm such that changes in osmotic pressure within the hydrogel are accompanied by changes in pressure exerted on the diaphragm;
• analyte binding molecules immobilized within the hydrogel;
• analyte molecules immobilized within the hydrogel;
• and
• a pressure transducer operatively engaged to the diaphragm.

A method for using a biosensor to measure the concentration of free molecules of an analyte in a fluid, including:

• a first step of providing a biosensor comprising:
• a rigid, biocompatible enclosure having an open end and a closed end, the open end being covered by a semipermeable membrane;
• a diaphragm positioned between the semipermeable membrane and the closed end such that changes in osmotic pressure within the hydrogel are accompanied by changes in pressure exerted on the diaphragm;
• a polymeric hydrogel having pendant moieties which are charged at physiological pH, the hydrogel being enclosed between the semipermeable membrane and the diaphragm such that changes in osmotic pressure within the hydrogel are accompanied by changes in pressure exerted on the diaphragm;
• analyte binding molecules immobilized within the hydrogel;
• analyte immobilized within the hydrogel, and
• osmotic pressure sensing means operatively engaged to the diaphragm for sensing the osmotic pressure exerted thereon and providing a data signal reflective thereof;
• a second step of providing computing means connected to receive the data signal, compare it to a predetermined calibration curve of osmotic pressure vs, concentration of free analyte molecules, and output a concentration value;
• a third step of inserting the biosensor into the fluid and allowing sufficient time for free analyte molecules to diffuse to equilibrium within the hydrogel;
• and
• a fourth step of reading the concentration value output by the computing means.