High Precision Scanning of Encoded Hydrogel Microparticles

Abstract

Techniques are provided for high precision scanning of hydrogel microparticles. The high precision is achieved by one or more modifications to the microparticle composition, or microfluidics apparatus that align the microparticles in a detection channel, or method of preparing a sample for introduction into the apparatus, or some combination. An apparatus comprises a body structure having formed therein a central channel and multiple focusing channels in fluid communication with the central channel through multiple junctions. A width of the central channel is smaller in a portion downstream of each junction. A particle comprises a hydrogel matrix and a probe molecule. The particle has an aspect ratio greater than about three. A method includes loading into a sample fluid inlet a mixture, wherein a number of particles lies within a range from about 5 to about 10 particles/μl.

1 . A particle comprising a hydrogel matrix and a probe molecule, wherein:
 a greatest particle dimension is less than about 500 micrometers (μm, 1 μm=10 −6  meters);   an aspect ratio of length to width of the particle is greater than about three; and   the probe molecule is selected to bind to a target molecule.   
     
     
         2 . The particle as recited in  claim 1 , wherein a first longitudinal portion of the particle is encoded with a plurality of thickness variations. 
     
     
         3 . The particle as recited in  claim 2 , wherein the first longitudinal portion is more rigid and less porous than a different second longitudinal portion of the particle. 
     
     
         4 . The particle as recited in  claim 3 , wherein the probe molecule is disposed only in the more porous hydrogel matrix in the different second longitudinal portion. 
     
     
         5 . The particle as recited in  claim 2 , further comprising a fluorescent entity loaded into the first longitudinal portion. 
     
     
         6 . The particle as recited in  claim 3 , wherein the hydrogel matrix in the first longitudinal portion comprises more Poly(ethylene glycol) (700) diacrylate and less Poly(ethylene glycol) (200) than does the hydrogel matrix in the second longitudinal portion. 
     
     
         7 . The particle as recited in  claim 3 , wherein:
 the hydrogel matrix in the first longitudinal portion comprises about 20% Poly(ethylene glycol) (700) diacrylate and about 20% Poly(ethylene glycol) (200) called DA30; and   the hydrogel matrix in the second longitudinal portion comprises about 10% Poly(ethylene glycol) (700) diacrylate and about 30% Poly(ethylene glycol) (200) called DA20.   
     
     
         8 . The particle as recited in  claim 2 , wherein the plurality of thickness variations vary horizontally on a scale matched to a scanning window of an apparatus to decode the encoded variations. 
     
     
         9 . The particle as recited in  claim 1 , wherein the aspect ratio is about 3.4. 
     
     
         10 . The particle as recited in  claim 2 , wherein the first longitudinal portion is about half the length of the hydrogel body. 
     
     
         11 . The particle as recited in  claim 1 , wherein the width is in a range from about 10 μm to about 80 μm and the length is in a range from about 80 μm to about 300 μm. 
     
     
         12 . A method comprising
 a) providing an apparatus comprising a body structure having formed therein a plurality of microfluidic channels comprising a central channel in fluid communication with a sample fluid inlet and a plurality of focusing channels in fluid communication with the central channel through a plurality of junctions;   b) providing a plurality of particles comprising hydrogel bodies sized to fit in the central channel, wherein each hydrogel body comprises a first longitudinal portion encoded with a plurality of thickness variations and a probe molecule, wherein the probe molecule is selected to bind to a target molecule and is associated with a particular plurality of thickness variations, and wherein the plurality of fabricated particles includes a plurality of different probe molecules;   c) loading into the sample fluid inlet a mixture of a test sample with the plurality of particles, wherein a number of particles in the mixture lies within a range from about 5 particles per microliter (particles/μl, 1 μl=10 −6  liters) to about 10 particles/μl;   d) detecting optical emissions from particles of the plurality of fabricated particles in the central channel downstream of a last junction of the plurality of junctions; and   e) determining presence of a target in the test sample based on the detected optical emissions.   
     
     
         13 . The method as recited in  claim 12 , further comprising applying a first pressure at the sample fluid inlet and a second pressure at a focusing fluid inlet in fluid communication with the plurality of focusing channels so that a sum of flow rates through the plurality of focusing channels is about equal to a flow rate of the sample fluid inlet. 
     
     
         14 . The method as recited in  claim 13 , wherein the sample fluid inlet is the same as the focusing fluid inlet and the first pressure is equal to the second pressure. 
     
     
         15 . The method as recited in  claim 12 , wherein the number of particles in the mixture is about 7.5 particles per μl.