EFIRM electrochemical
biosensing technology.

The molecules in the animation

Cell-free DNA (cfDNA) consists of DNA fragments found outside cells in body fluids. Circulating tumor DNA (ctDNA) is the tumor-derived fraction of that pool. Detecting a selected mutation requires a target-specific assay; measuring total cfDNA alone does not identify its tumor origin.

Mononucleosomal ctDNA (mnctDNA) refers to tumor-derived fragments associated with a single nucleosome, the protein structure around which DNA is packaged. Cell-free mononucleosomal fragments commonly cluster near 166 base pairs, but their lengths vary. Ultrashort ctDNA (usctDNA) describes a shorter population, including fragments of only a few dozen nucleotides in published studies. Definitions and size cutoffs differ between studies. These fragments may still retain a mutation-bearing target sequence. Base pairs (bp) describe paired DNA length; nucleotides (nt) describe the units in a strand.

Two routes from a target to a signal

Droplet digital PCR (ddPCR) partitions a sample into droplets, amplifies a selected DNA region and estimates target abundance from positive and negative droplets. A fragment must retain the sequence needed by that assay, including the relevant primer-binding sites. Fragments shorter than the required amplification region may be missed. This is a design constraint, not a universal inability of ddPCR to detect short DNA: specialized short-target and stem-loop assays can detect ultrashort fragments.

EFIRM (Electric Field-Induced Release and Measurement) combines field-assisted molecular interactions, target-specific probe recognition and electrochemical measurement. In selected published DNA assays, hybridization at the sensor surface produces an enzyme-mediated electrical signal without PCR amplification of the target. Some ultrashort fragments that retain the required recognition sequences can therefore contribute to the measurement. Capture efficiency and signal generation remain dependent on the assay, sequence and specimen.

How fragment length changes the signal

At a fixed total amount of ctDNA, increasing the ultrashort fraction can reduce the number of molecules accessible to an assay requiring a longer target region. For teaching only, the model assumes that all fragments retain the EFIRM recognition sites, while only the longer fragments retain the target region required by the illustrated ddPCR design. In this idealized example, 50 target copies with a 70% ultrashort fraction yield 15 accessible copies for the illustrated conventional ddPCR design and 50 for the illustrated EFIRM design. When the total falls to 10, the corresponding model inputs become 3 and 10.

The shared threshold of 6 accessible copies per reaction is a teaching assumption, not a clinical specification. Bars and stars represent relative model signals, not interchangeable physical measurements; EFIRM current is not itself a direct DNA copy count. Real detection is probabilistic at low copy numbers and depends on sample volume, recovery, fragment structure, background, controls and assay-specific validation. A result below a detection threshold does not prove that the target is absent.

How could researchers evaluate complementarity?

A matched research comparison would control specimen handling and input volume, test standards carrying the same variant across different fragment lengths, and include blanks, wild-type controls and repeated low-copy measurements. Recovery, specificity, reproducibility and assay-specific detection limits should be assessed. Comparing EFIRM with both the relevant conventional ddPCR assay and a suitable short-target design can help distinguish fragment coverage from other analytical effects. This is a proposed evaluation approach, not a completed clinical validation.

Potential relevance for liquid-biopsy research

Fragment-aware assay design may help recover mutation information that would otherwise be missed when tumor-derived DNA is scarce. This is relevant to research on low-abundance variants and longitudinal molecular monitoring. It also helps explain why two platforms can disagree on the same specimen without either result alone establishing the true disease state. The animation does not demonstrate earlier cancer diagnosis, reliable residual-disease detection or improved patient outcomes; those uses require their own clinical evidence.

Research context: A 2020 EGFR study investigated length-dependent detection and included paired plasma and saliva specimens from 13 patients with non-small-cell lung cancer. A 2024 study used a specialized 42-bp stem-loop ddPCR assay for HPV16-associated urinary ctDNA; this was a different target and specimen context, not a head-to-head comparison with EFIRM. These findings support assay-specific comparisons rather than a universal ranking of technologies. EZLife products are presented for research use only, not for use in diagnostic procedures.

Read the 2020 EFIRM fragment study · Read the 2024 ultrashort ddPCR study