Sample flows through a microfluidic channel over a sensor surface coated
with immobilised recognition elements (antibodies/aptamers). Each analyte
molecule that reaches a free site can bind; occupied sites are transduced
into an electrical or optical signal read out on the strip at the channel
exit. Once the signal crosses the threshold, the chip reports a positive
result.
binding rate = k_on · [analyte] · (1 − θ) (θ = fraction sites occupied)
signal(t) = θ(t) × gain(sensor type)
LOD ≈ concentration at which signal ≈ threshold at steady flow
- Analyte concentration — how much target molecule is in the sample; higher concentration binds sites faster.
- Flow rate — how quickly sample is delivered across the sensor surface.
- Sensor type — electrochemical gives a fast, noisier signal; optical gives a slower but cleaner one.
- Detection threshold — signal level that must be crossed before the chip calls a positive result.
This mirrors real point-of-care assay design: sensitivity (how low a
concentration triggers detection) is set by the balance between binding
kinetics, flow delivery and the chosen threshold.