Pencil-Drawn Chemiresistive Sensor for Free Chlorine in Water
Bibliographic record
Abstract
Free chlorine concentration in drinking water is an important control parameter throughout the distribution network, since both too-low and too-high concentrations can lead to health hazards, with 0.5-2 ppm being a typically acceptable range. Although colorimetric and electrochemical methods exist for measuring free chlorine, they require either the addition of chemicals during manual sampling or maintenance intensive instrumentation, such as reference electrodes. We have previously demonstrated a simple, reliable, reagent-fee solid-state chemiresistive sensor for continuous monitoring of aqueous free chlorine concentrations based on a functionalized carbon nanotube film. Here, we show that the same sensing principle can be translated to lower cost materials-as simple as a line drawn between two contacts using a free IKEA pencil. While IKEA (HB grade, about 70% graphite) pencils work well enough for quantitative free chlorine sensors, the use of 9B grade pencils (90% + graphite) results in higher sensitivity. Bare pencil line sensors show a nonselective response to a wide range of aqueous species; pencil lines functionalized with a redox-active aniline oligomer (phenyl-capped aniline tetramer), however, are highly selective to oxidant species, namely free chlorine, in a demonstrated range of 0.06-60 ppm. The resulting sensors are cost-effective, durable, resettable, reusable, and resistant to fouling. In contrast to electrochemical sensors, they do not require the use of a reference electrode. They can be operated continuously online for drinking water quality monitoring.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".