Microdroplet dispensing for a medical diagnostic device

Abstract

A medical diagnostic device has a non-absorbent substrate that has a hydrophilic target area on which a reagent is deposited by non-impact printing of microdroplets. During deposition, the device is moved relative to the stream of microdroplets to form a substantially uniform reagent layer on the substrate. The device is particularly well adapted for measuring blood coagulation times. In a preferred embodiment, coagulation times are determined by monitoring the optical transmission of light through the target area as an applied blood sample interacts with the reagent.

We claim:  
     
         1 . A method for preparing a medical diagnostic reagent device, comprising the steps of 
 a) providing a non-absorbent substrate, having on its surface at least one hydrophilic target area,    b) providing from a nonimpact print head onto a point within the target area a pulsed stream of microdroplets of a diagnostic reagent liquid.    c) moving the stream relative to the substrate, and    d) repeating steps b) and c) at least enough times to provide a substantially uniform layer of the liquid over the target area.    
     
     
         2 . The method of  claim 1 , in which the substrate comprises a substantially planar sheet.  
     
     
         3 . The method of  claim 1 , in which the substrate comprises a thermoplastic sheet.  
     
     
         4 . The method of  claim 1 , in which each of the at least one target areas has a water contact angle of no more than about 60°.  
     
     
         5 . The method of  claim 1 , in which the print head is a thermal ink-jet print head.  
     
     
         6 . The method of  claim 1 , in which the reagent liquid comprises thromboplastin.  
     
     
         7 . The method of  claim 2 , in which the stream travels in a direction that is substantially perpendicular to the substrate, and the stream is moved relative to the substrate by moving the substrate in a direction that is substantially perpendicular to the direction of stream travel.  
     
     
         8 . The method of  claim 1 , in which the stream passes through a hole in a sheet that is positioned between the dispenser and substrate.  
     
     
         9 . The method of  claim 8 , in which the sheet has a hydrophobic surface that faces the dispenser.  
     
     
         10 . The method of  claim 9 , in which the reagent comprises a colorant.  
     
     
         11 . A diagnostic reagent device for measuring an analyte concentration or characteristic of a biological fluid, including a non-absorbent substrate comprising 
 a) a sample application area for accepting a sample of the biological fluid for analysis and    b) a predetermined hydrophilic reagent area, onto which has been applied, by nonimpact printing, a diagnostic reagent liquid that interacts with the sample to cause in the sample a physically-measurable change that can be related to the analyte concentration or characteristic of the fluid.    
     
     
         12 . The device of  claim 11 , in which the sample application area and reagent area substantially coincide.  
     
     
         13 . The device of  claim 11 , further comprising means for conveying the sample from the application area to the reagent area.  
     
     
         14 . The device of  claim 11 , in which the sample application area is hydrophilic.  
     
     
         15 . The device of  claim 11 , in which the substrate comprises a substantially transparent planar sheet.  
     
     
         16 . The device of  claim 11 , in which the substrate comprises a substantially transparent thermoplastic sheet.  
     
     
         17 . The device of  claim 11 , in which the reagent liquid comprises thromboplastin.  
     
     
         18 . The device of  claim 11 , in which the reagent liquid comprises a colorant.  
     
     
         19 . The device of  claim 13 , in which the means for conveying the sample from the application area to the reagent area comprises a top layer, separated from the substrate by an intermediate layer that has a through hole and adjoining channel cut into it, the top layer, intermediate layer, and substrate forming a bladder that, when compressed, and released causes in the channel a reduced pressure that draws blood into the reagent area.  
     
     
         20 . The device of  claim 19 , in which the top layer has a hydrophobic surface facing the substrate, at least in the channel and reagent area.