Microfluidic systems

1. A microfluidic system comprising:

a) a microfluidic chip comprising a microfluidic channel opening onto a chip inlet and a chip outlet, wherein the channel comprises:

(i) a sensing area having a volume between about 0.1 nl and about 10 nl; and

(ii) a fluid delivery area adapted to deliver fluid to the sensing area; and

b) a fluidic adaptor adapted to hold the microfluidic chip and comprising a fluidic adaptor channel opening onto an adaptor inlet and an adaptor outlet, wherein the fluidic adaptor channel is adapted to receive a pipette tip through the adaptor inlet, wherein the pipette tip is adapted to deliver between 0.1 microliter and 10 microliters of fluid and the adaptor outlet is directly connected to the chip inlet, wherein receipt of the pipette tip into the adaptor channel creates a direct fluid path between the pipette tip and the microfluidic channel;

wherein said adaptor channel and the fluid delivery area have a volume of no more than 1 microliter and a length of no more than 7 millimeters; and

wherein the microfluidic system is configured for sensing in the sensing area by interferometry.

2. The microfluidic system of claim 1 wherein the microfluidic chip comprises glass.

3. The microfluidic system of claim 1 wherein the microfluidic chip comprises a material selected from glass, quartz, borosilicate, silica and a polymeric material.

4. The microfluidic system of claim 1 wherein the microfluidic chip comprises a material selected from polyacrylate, cyclic olefin copolymer, polydimethyl siloxane, polycarbonate, and polymethyl methacrylate.

5. The microfluidic system of claim 1 wherein the microfluidic chip comprises a second microfluidic channel opening onto a chip inlet and a chip outlet, wherein the channel comprises: (i) a sensing area having a volume between about 0.1 nl and about 10 nl; and (ii) a fluid delivery area adapted to deliver fluid to the sensing area; and

wherein the fluidic adaptor comprises a second fluidic adaptor channel opening onto a second adaptor inlet and a second adaptor outlet, wherein the fluidic adaptor channel is adapted to receive a second pipette tip through the second adaptor inlet, wherein the second pipette tip is adapted to deliver between 0.1 microliter and 10 microliters of fluid and the second adaptor outlet is directly connected to the chip inlet, wherein receipt of the pipette tip into the adaptor channel creates a direct fluid path between the pipette tip and the microfluidic channel; and wherein receipt of the pipette tip into the adaptor channel creates a direct fluid path between the pipette tip and the microfluidic channel.

6. The microfluidic system of claim 1 wherein the microfluidic chip comprises a cover plate bonded to an etched plate comprising a microfluidic channel.

7. The microfluidic system of claim 1 further comprising a pipette tip mated with the adaptor channel to maintain a distance of no more than 7 mm between sample introduction via the pipette and the sensing area.

8. The microfluidic system of claim 1 wherein the adaptor comprises a spring or screw adapted to hold the chip in the adaptor.

9. The microfluidic system of claim 1 configured such that when 1 microliter of a solution of 10 picomolar bovine serum albumin in phosphate buffered saline is delivered from a micropipette tip through the adaptor and adaptor channel to the sensing area, the loss of BSA concentration is no more than 5%.

10. The microfluidic system of claim 9 wherein the loss is no more than 1%.

11. The microfluidic system of claim 9 wherein the loss is no more than 0.05%.

12. The microfluidic system of claim 9 wherein the loss is no more than 0.01%.

13. The microfluidic system of claim 1 wherein the microfluidic channel has a cross-sectional area of no more than 0.3 mm 2 .

14. The microfluidic system of claim 1 wherein the microfluidic channel has a cross-sectional area of no more than 0.003 mm 2 .

15. A method comprising:

providing a microfluidic system of claim 1 ;

introducing a sample having a volume between 0.1 microliter and 10 microliters into the adaptor channel;

moving the sample through the delivery channel into a sensing area; and

sensing analyte in the sensing area by interferometry.

16. The method of claim 15 comprising introducing a sample having a volume between 0.5 to 5 microliters.

17. The method of claim 15 comprising introducing a sample having a volume between 0.8 microliters to 3 microliters.

18. The method of claim 15 comprising introducing a sample having a volume of about 1 microliter.