Absolute quantification of real-time PCR data with stage signal difference analysis

TL;DR

This paper introduces a novel qPCR quantification method that monitors fluorescence changes at each thermal cycle stage to accurately determine nucleic acid amounts, avoiding traditional efficiency assumptions.

Contribution

It develops a new absolute quantification approach by directly calculating PCR efficiency changes from fluorescence signals during thermal cycles.

Findings

Efficiency change during PCR is complex and non-monotonic.

The new method accurately quantifies nucleic acids without efficiency modeling.

Classical threshold methods are supplemented by this more precise approach.

Abstract

Real-time PCR, or Real-time Quantitative PCR (qPCR) is an effective approach to quantify nucleic acid samples. Given the complicated reaction system along with thermal cycles, there has been long-term confusion on accurately calculating the initial nucleic acid amounts from the fluorescence signals. Although many improved algorithms had been proposed, the classical threshold method is still the primary choice in the routine application. In this study, we will first illustrate the origin of the linear relationship between the threshold value and logarithm of the initial nucleic acid amount by reconstructing the PCR reaction process with stochastic simulations. We then develop a new method for the absolute quantification of nucleic acid samples with qPCR. By monitoring the fluorescence signal changes in every stage of the thermal cycle, we are able to calculate a representation of the step-wise efficiency change. This is the first work calculated PCR efficiency change directly from the fluorescence signal, without fitting or sophisticated analysis. Our results revealed that the efficiency change during the PCR process is complicated and can not be modeled simply by monotone function model. Based on the calculated efficiency, we illustrate a new absolute qPCR analysis method for accurately determining nucleic acid amount. The efficiency problem is completely avoided in this new method.