I have run enough diagnostic assays to know one thing for certain: a result on the screen is never the whole story. Somewhere behind every positive and every negative sits the question of whether the test got it right.
Think of a village watching for a wolf. Every time the village relies on a lookout, that lookout gets two chances to be wrong. The lookout can cry wolf, or the lookout can miss the wolf. A diagnostic test is no different.
Crying wolf: the false positive
There was no wolf, but the test said it saw one. That is a false positive, and the property that protects you from it is called specificity.
A highly specific test only raises the alarm when the target is truly there. A poorly specific one panics over shadows. In a clinic, that can mean unnecessary treatment, anxiety, and a lot of wasted resources.
Missing the wolf: the false negative
Now the opposite. The wolf was right there, but the test did not detect it. That is a false negative, and the property that protects you from it is called sensitivity.
This is the quieter failure. Nobody panics, which is exactly the problem. A patient who is infected goes home reassured, and the infection moves on.
How CRISPR helps with both
In a recent interview, Feng Zhang, one of the pioneers of CRISPR technology, explained that CRISPR-based diagnostics can improve both metrics at once. His reasoning is worth unpacking, because the two improvements come from two different steps.
Better sensitivity (fewer missed wolves). The sample is first concentrated and then amplified, usually by PCR or an isothermal method. CRISPR then adds a second layer of amplification on top, called collateral activity. Once the CRISPR enzyme recognises its target, it starts cutting nearby nucleic acids indiscriminately, including a reporter molecule that gives off a signal. The result is a stronger signal from the same amount of starting material. It is a bit like turning up the volume on a whisper.
In the SHERLOCK platform that Zhang’s group developed, this enzyme is Cas13, which targets RNA (Gootenberg et al., 2017). Zhang does not name the enzyme in this interview, so that detail comes from the original paper.
Better specificity (fewer false alarms). Amplification already checks for the viral sequence once. CRISPR then checks again, because the guide RNA has to recognise the sequence before the signal is produced. A false result has to survive both checks to count. It is the friend who asks “are you sure?” before you hit send.
Why this matters outside the lab
Zhang points out that CRISPR diagnostics are being developed for point-of-care and at-home use. For anyone working in places where a full molecular lab is not around the corner, that is the part that excites me most. A test that is both sensitive and specific, and that does not need a lab full of equipment, changes who gets an answer and how quickly.
Quick summary
| The wolf | What it means | Technical term | How CRISPR helps |
|---|---|---|---|
| Cry wolf (Specificity) | It was not there, but the test said it saw it | False positive (specificity problem) | Target checked twice: amplification, then CRISPR detection |
| Miss the wolf (Sensitivity) | It was there, but the test did not detect it | False negative (sensitivity problem) | Amplify first, then Cas13 collateral cutting boosts the signal |
Related Content
CRISPR-Cas9 Explainer: How It Works, Guide RNA and PAM: https://adwoabiotech.blogspot.com/2026/11/crispr-cas9-explained-guide-rna-pam.html
Reference
Gootenberg, J. S., Abudayyeh, O. O., Lee, J. W., Essletzbichler, P., Dy, A. J., Joung, J., Verdine, V., Donghia, N., Daringer, N. M., Freije, C. A., Myhrvold, C., Bhattacharyya, R. P., Livny, J., Regev, A., Koonin, E. V., Hung, D. T., Sabeti, P. C., Collins, J. J., & Zhang, F. (2017). Nucleic acid detection with CRISPR-Cas13a/C2c2. Science, 356(6336), 438–442. https://doi.org/10.1126/science.aam9321
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