# Enhancing the performance of DNA surface-hybridization biosensors through target depletion

## TL;DR

This paper analyzes how target depletion affects DNA biosensor hybridization, revealing that depletion can significantly enhance sensitivity and enable detection of very low-abundance mutant sequences.

## Contribution

It extends the Langmuir model to account for target depletion, demonstrating improved detection sensitivity and sample enrichment in DNA biosensors.

## Key findings

- Depletion enhances biosensor sensitivity by up to three orders of magnitude.
- Kinetics show non-monotonic adsorption behavior in the depletion regime.
- Sample enrichment of mutant sequences is possible through target depletion.

## Abstract

DNA surface-hybridization biosensors utilize the selective hybridization of target sequences in solution to surface-immobilized probes. In this process, the target is usually assumed to be in excess, so that its concentration does not significantly vary while hybridizing to the surface-bound probes. If the target is initially at low concentrations and/or if the number of probes is very large and have high affinity for the target, the DNA in solution may get depleted. In this paper we analyze the equilibrium and kinetics of hybridization of DNA biosensors in the case of strong target depletion, by extending the Langmuir adsorption model. We focus, in particular, on the detection of a small amount of a single-nucleotide "mutant" sequence (concentration $c_2$) in a solution, which differs by one or more nucleotides from an abundant "wild-type" sequence (concentration $c_1 \gg c_2$). We show that depletion can give rise to a strongly-enhanced sensitivity of the biosensors. Using representative values of rate constants and hybridization free energies, we find that in the depletion regime one could detect relative concentrations $c_2/c_1$ that are up to three orders of magnitude smaller than in the conventional approach. The kinetics is surprisingly rich, and exhibits a non-monotonic adsorption with no counterpart in the no-depletion case. Finally, we show that, alongside enhanced detection sensitivity, this approach offers the possibility of sample enrichment, by substantially increasing the relative amount of the mutant over the wild-type sequence.