DNA Hybridization Biosensor

DNA-Hybridization Biosensor

Stringency temperature 55 °C

Probe density Medium

Mismatched (off-target) fraction 30%

Target concentration Medium

Signal (matched)

–

False signal

–

Specificity

–

Bound / total

–

How it works

Short single-stranded DNA probes are immobilized on the sensor surface. Fluorescently labeled target strands diffuse past; a perfectly complementary target zips onto its probe and stays bound (base pairs are stable), while a strand with one or more mismatches binds only weakly and unzips again — unless the solution is too "loose" (low temperature = low stringency), in which case mismatches stick around too and generate a false signal.

P(stay bound) = 1 / (1 + exp((T − Tm) / k))
Tm(matched)    ≈ high      Tm(mismatched) ≈ Tm − ΔTm·mismatches
Specificity    = signal_matched / (signal_matched + signal_mismatched)

Stringency temperature — the wash/hybridization temperature. Higher temperature melts weak (mismatched) duplexes off first, raising specificity but eventually melting the matched signal too.
Probe density — more capture sites on the surface raise the maximum signal (sensitivity) but also raise crowding, which can trap mismatches non-specifically.
Mismatched fraction — how much of the target pool is a near-relative (off-target) sequence rather than the true target — the real-world contamination/cross-reactivity challenge.
Target concentration — more target molecules in solution means faster, more complete binding — but also a faster false-signal rise if stringency is too low.

Real-world relevance: this temperature-controlled discrimination between a perfect match and a one- or two-base mismatch is exactly how DNA microarrays, qPCR probes and point-of-care pathogen gene tests tell a true positive from a false one.

Signal vs. time

Probe (surface) Matched target — bound Mismatched target — bound Free target (unbound)

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