Nanomaterial sensors: high sensitivity is the easy half, selectivity is the hard half

How it works

A chemiresistive sensor reports a change in electrical resistance when something adsorbs on its surface. The review of selectivity in these devices describes the mechanism for n-type semiconductors as adsorbed oxygen species undergoing redox reactions with the gas, which makes the limitation structural rather than incidental: different gases act on the same sites, so the device measures “something adsorbed and transferred charge”, not “this analyte is present”. The review states plainly that such sensors struggle to detect target gases selectively in mixtures because of cross-sensitivity. It also reports that excessive defect engineering — often the route to higher sensitivity — can increase noise, cause baseline drift and reduce carrier mobility, and that humidity remains a persistent interferent. The finding a reader should carry away is the one about the literature itself: a standardised approach for assessing selectivity is lacking, so response-ratio indicators are poorly comparable between studies. This section covers the transduction and the evidence question. Event-driven and neuromorphic sensing, where the interesting part is how the signal is encoded and computed rather than how the surface responds, belongs to the neuromorphic section.

A concrete case

A device is reported with a detection limit in the parts-per-billion range for a target gas. The figure may be exactly right in dry air against that gas alone, and tell you very little about a humid room containing several reducing gases — a condition the review says there is no standard way to test.

Questions worth asking

• Ask what else was in the gas stream during the reported measurement, and at what humidity.
• Ask how selectivity was quantified, and against which interferents — then ask whether another paper’s number was computed the same way.
• Ask for baseline drift over the intended deployment period, not just a response curve.
• Treat a detection limit measured against a single analyte in dry air as a ceiling, not an operating specification.

Sources

• Liu et al. — Advancements and Strategies for Selectivity Enhancement in Chemiresistive Gas Sensors (Nanomaterials, 2025) ↗

  Chemiresistive sensing works through non-specific surface chemistry — for n-type semiconductors, adsorbed oxygen species and redox reactions with the analyte — so different gases can act on the same sites, and the review states such sensors struggle to detect target gases selectively in mixtures because of cross-sensitivity. It reports that excessive defects can increase noise, cause baseline drift and reduce carrier mobility, that humidity is a persistent interferent, and that a standardised approach for assessing selectivity is lacking, leaving response-ratio indicators poorly comparable between studies.

  Boundary: A review of the chemiresistive literature. It gives no performance figure for any commercial sensor and certifies no device, and the absence of a standard selectivity method is a statement about the field, not about a particular product’s quality.

  Locator, anchor and reuse basis

  Read at: §1 Introduction; §2 Gas Sensing Mechanism; §3.1.2 Defects Generation. Inspected 2026-09-20. Open-access review; paraphrased and linked, with short attributed wording only.

  Verify by searching the source for: a standardized approach for assessing gas selectivity is lacking. If that phrase is not there, or does not carry the meaning stated above, this citation is wrong and we want to know.

Continue

• Structure–property claims need the mechanism, not the correlation
• Reading a nanomaterial datasheet or demonstration claim
• One batch is one batch

Elsewhere on this site

• Neuromorphic and biocomputing: event-driven sensing and in-memory computation