What Is Digital PCR?
Digital polymerase chain reaction, commonly abbreviated as dPCR, is a nucleic-acid amplification and quantification technology designed to measure target DNA or RNA molecules by dividing a sample into a large number of individual reaction partitions.
Unlike conventional quantitative PCR, where amplification is monitored through fluorescence during cycling, dPCR generally determines whether individual partitions are positive or negative after amplification. The resulting partition counts can then be used to estimate the concentration of the target.
dPCR is essentially a counting-based approach to PCR. A sample is divided into many small reactions, amplified, and then analysed according to which reactions contain detectable target molecules.
Show Details — Why is it called “digital” PCR?
The term “digital” refers to the classification of individual partitions into discrete states, typically positive or negative for the target signal.
Instead of relying primarily on the continuous amplification curve used in qPCR, dPCR converts the measurement into a collection of individual molecular detection events.
The Principle Behind dPCR
The fundamental concept behind dPCR is partitioning. A conventional PCR mixture contains many target molecules in a single reaction. In dPCR, that mixture is distributed across numerous smaller reaction compartments.
Some partitions contain one or more target molecules, while others contain no target. Following amplification, fluorescence detection allows the instrument to distinguish between positive and negative partitions.
Three fundamental stages
How Does a dPCR Workflow Work?
Although individual platforms differ in their chemistry and partitioning technology, a typical dPCR experiment follows the general workflow below.
1. Prepare the reaction
The reaction contains the nucleic-acid template, primers, fluorescent probes or other detection chemistry, polymerase and the required reaction components.
2. Partition the reaction
The reaction mixture is divided into a large number of independent partitions. Depending on the platform, these may be droplets, wells or other microfluidic reaction chambers.
3. Perform PCR amplification
The partitions undergo thermal cycling. Target molecules present in individual partitions are amplified.
4. Detect fluorescence
After amplification, the partitions are analysed for fluorescence. The resulting signals allow the system to identify positive and negative reactions.
5. Calculate target concentration
The number of positive and negative partitions is analysed statistically to estimate the concentration of the target nucleic acid.
Show Details — What happens inside a partition?
A partition may contain zero, one, or multiple copies of the target molecule. After amplification, target- containing partitions generally produce a measurable fluorescence signal.
Because the distribution of molecules among partitions follows statistical principles, the observed positive fraction can be used to estimate the original target concentration.
How Does dPCR Provide Absolute Quantification?
One of the defining characteristics of dPCR is its ability to estimate the absolute concentration of a target from the distribution of positive and negative partitions.
The analysis takes into account the total number of partitions and the fraction that contain detectable target. Statistical correction is important because a partition can contain more than one target molecule.
“Absolute quantification” does not mean that experimental controls, assay validation or appropriate reference materials are unnecessary. Good experimental design and validated assays remain essential for reliable results.
dPCR vs qPCR
dPCR and qPCR are both PCR-based technologies, but their approaches to measurement and quantification are different.
| Feature | qPCR | dPCR |
|---|---|---|
| Measurement | Amplification kinetics | Endpoint partition analysis |
| Quantification | Commonly relative or calibration-based | Absolute concentration can be estimated |
| Sample format | Typically one reaction volume | Many individual partitions |
| Standard curve | Commonly used for absolute quantification | Generally not required for concentration estimation |
| Typical strength | Fast and established quantitative PCR workflow | Partition-based absolute quantification and rare-target analysis |
Show Details — Which technology should researchers use?
There is no universal winner. The appropriate technology depends on the research question, assay design, sample type, required sensitivity, throughput and available instrumentation.
qPCR remains highly useful for routine quantitative workflows, while dPCR can offer particular advantages when absolute quantification or rare target detection is important.
Applications of Digital PCR
dPCR is used across molecular biology, genomics, biotechnology and research applications where sensitive and quantitative nucleic-acid measurement is required.
Genetic Variation
Research applications can include measurement of genetic variants and low-frequency molecular targets.
Copy Number Analysis
dPCR can be used to investigate differences in the number of copies of specific genomic targets.
Liquid Biopsy Research
Partition-based analysis can support investigation of low-abundance nucleic acids in biological samples.
Pathogen Research
Digital PCR can support quantitative detection of specific microbial or viral nucleic-acid targets.
Frequently Asked Questions
What does dPCR stand for?
dPCR stands for digital polymerase chain reaction, a PCR-based technology that partitions samples into numerous individual reactions for endpoint analysis.
Is dPCR the same as qPCR?
No. Both use PCR amplification, but qPCR generally monitors fluorescence during amplification, whereas dPCR typically analyses endpoint fluorescence across individual partitions.
Does dPCR require a standard curve?
A conventional standard curve is generally not required for dPCR-based absolute concentration estimation because quantification is derived from partition statistics.
Why is partitioning important?
Partitioning distributes target molecules among many independent reactions, allowing the system to count positive and negative partitions.
Is dPCR more sensitive than qPCR?
dPCR can provide advantages for certain low-abundance or rare-target applications, but assay performance depends on target, chemistry, sample quality and experimental design.
Scientific References
- Hindson BJ, et al. High-throughput droplet digital PCR system for absolute quantitation of DNA copy number. Analytical Chemistry.
- Huggett JF, et al. The digital MIQE guidelines: Minimum Information for Publication of Quantitative Digital PCR Experiments.
- Whale AS, Huggett JF. Digital PCR as a method for absolute quantification of nucleic acids.
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