Crowded sensor

1. A sensing device comprising:

a first sidewall and a second sidewall, wherein a fluid channel is defined between the first sidewall and the second sidewall;

a sensor having a surface defining at least a portion of the fluid channel;

an analyte capture ligand bound to the surface of the sensor; and

a crowding agent separately bound to the surface of the sensor and configured to slow kinetics of target analyte binding to the analyte capture ligand,

wherein the crowding agent does not specifically bind to the target analyte.

2. The sensing device of claim 1 , wherein the sensor comprises a bulk acoustic wave resonator structure.

3. The sensing device of claim 1 , wherein the first and second sidewalls are formed from a single structure having opposing surfaces.

4. The sensing device of claim 1 , wherein a molar ratio of the crowding agent to the analyte capture ligand is from about 50 to 1 to about 0.1 to 1.

5. The sensing device of claim 1 , wherein a molar ratio of the crowding agent to the analyte capture agent is from about 2 to 1 to about 0.25 to 1.

6. The sensing device of claim 1 , wherein the crowding agent comprises a polymer.

7. The sensing device of claim 1 , wherein the crowding agent comprises one or more of polyethylene glycol (PEG), a branched polymer formed by copolymerization of sucrose and epichlorohydrin, dextran, polyvinyl alcohol, a polypeptide, and a polynucleic acid.

8. The sensing device of claim 1 , wherein the crowding agent comprises a non-organic structure.

9. The sensing device of claim 1 , wherein the crowding agent comprises silicon.

10. The sensing device of claim 9 , wherein the silicon forms pillars extending from the surface of the bulk acoustic resonator structure.

11. A sensing device comprising:

a first sidewall and a second sidewall, wherein a fluid channel is defined between the first sidewall and the second sidewall;

a sensor having a surface defining at least a portion of the fluid channel;

an analyte capture ligand bound to the surface of the sensor;

a cover disposed over, and coupled to, the first and second sidewalls, wherein a surface of the cover defines at least a portion of the channel opposing the surface of the sensor; and

a crowding agent separately bound to a surface of the cover, the first sidewall, the second sidewall, or any combination thereof,

wherein the position and length of the crowding agent is sufficiently close to the surface of the bulk acoustic resonator for the crowding agent to slow kinetics of target analyte binding to the analyte capture ligand when a fluid sample composition comprising the target analyte is flowed through the channel and across the surface of the sensor, and

wherein the crowding agent does not specifically bind to the target analyte.

12. The sensing device of claim 11 , wherein the sensor comprises a bulk acoustic wave resonator structure.

13. The sensing device of claim 11 , wherein the first and second sidewalls are formed from a single structure having opposing surfaces.

14. The sensing device of claim 11 , comprising one or more gaps formed in the channel to allow larger molecules in the fluid sample composition to flow through the channel.

15. The sensing device of claim 11 , wherein a molar ratio of the crowding agent to the analyte capture ligand is from about 100 to 1 to about 0.01 to 1.

16. The sensing device of claim 11 , wherein the crowding agent comprises a polymer.

17. The sensing device of claim 11 , wherein the crowding agent comprises one or more of polyethylene glycol (PEG), ficoll, dextran, polyvinyl alcohol, a polypeptide, and a polynucleic acid.

18. The sensing device of claim 11 , wherein the crowding agent comprises a non-organic structure.

19. The sensing device of claim 11 , wherein the crowding agent comprises silicon.

20. The sensing device of claim 19 , wherein the silicon forms pillars extending from the surface of the bulk acoustic resonator structure.