Monitoring DNA amplification
A method and kits are provided for nucleic acid quantification and discrimination using surface plasmon resonance (SPR). The method provided is able to significantly enhance the detection limit and multiplex the discrimination assay using the melting properties of the target DNA on top of standard PCR reaction. By using the heating and cooling cycles of the polymerase chain reaction (PCR) or Ligation chain reaction (LCR), DNA is melted and hybridized onto the SPR sensor surface together with a nanoparticle label. Thus, during every cycle of DNA amplification, the quantity and type of target DNA can be monitored.
1. A method for real-time detection of a target nucleic acid in a sample, comprising the steps of:
a) providing a reaction chamber comprising
a mass-sensitive sensor, wherein the sensor is functionalized with a first nucleic acid probe that hybridizes to said target nucleic acid, and
metal nanoparticles functionalized with a second nucleic acid probe that hybridizes to said target nucleic acid, wherein said first and second probes bind to different regions of said target nucleic acid such that the first and second probes can hybridize simultaneously to said target nucleic acid,
b) adding a sample to the reaction chamber and performing, with the sensor being present within the reaction chamber, a nucleic acid amplification of the target nucleic acid using non-immobilized, non-metal functionalized probes complementary to the target nucleic acid, wherein during the annealing step of the amplification method, amplified target nucleic acid forms a complex with the first probe on the sensor and the second probe with the metal nanoparticles, and
c) determining during a denaturation step of the nucleic acid amplification reaction, the presence of the target nucleic acid at the sensor by measuring at the melting temperature of the complex formed in step b, the release of the amplified target nucleic acid from the sensor.
2. The method according to claim 1 , which is a multiplex assay for the detection of a plurality of different target nucleic acids, wherein for each of the different target nucleic acids, a specific set of a first nucleic acid probe on the sensor that hybridizes to a target nucleic acid and a second nucleic acid probe on the metal nanoparticles are provided, and wherein non-immobilized, non-metal functionalized amplification probes are provided to amplify all target nucleic acids, such that for each of the complexes of a different nucleic acid target and its corresponding first and second nucleic acid probe a different melting temperature is obtained, and wherein by measuring at the melting temperature of each of the different nucleic acid target complexes, the presence of each of the different target nucleic acids on the sensor is determined.
3. The method according to claim 2 , wherein the difference in melting temperature between each of the different complexes is at least 0.3° C.
4. The method according to claim 2 , wherein said first probes for the different target nucleic acids are immobilized on the same sensor surface.
5. The method according to claim 2 , wherein the difference in melting temperature between each of the different complexes is at least 1.5° C.
6. The method according to claim 1 , wherein said non-immobilized, non-metal functionalized probes for amplification are present in the reaction chamber prior to the addition of the sample.
7. The method according to claim 1 , wherein said metal nanoparticles are gold nanoparticles.
8. The method according to claim 1 , wherein said nucleic acid amplification is a Polymerase Chain Reaction.
9. The method according to claim 1 , wherein said nucleic acid amplification is a Ligation Chain Reaction (LCR).
10. The method according to claim 1 , comprising comparing each amplification cycle with a reference curve indicating nucleic acid concentration as a function of amplification cycles.
11. The method according to claim 10 , wherein said amplification cycles comprise at least one cycle in which melting rates are in a range between 0.1° C./s-1.5° C./s.
12. The method according to claim 10 , wherein the denaturation step of said amplification cycles is less than 5 seconds in duration.
13. The method according to claim 1 , wherein said mass-sensitive sensor is an optic sensor.
14. The method according to claim 13 , wherein said optic sensor is a fibre optic sensor.
15. The method according to claim 14 , wherein a refractive index at said fibre optic sensor is continuously measured during the amplification cycles of the nucleic acid amplification reaction.
16. The method according to claim 13 , wherein the melting temperature is determined by shifts in refractive index at specific temperatures.
17. The method according to claim 16 , comprising comparing the measurable shifts in the refractive index signals with a calibration curve indicating expected melting temperatures for each target nucleic acid.
18. The method according to claim 16 , wherein quantities of target nucleic acid are determined in real-time by counting amplification cycles needed to produce the measurable shift in refractive index.