needle in a haystack

Syllable breakdown

Dictionary meaning

an idiom describing a search task that is practically impossible or requires extraordinary effort because the object being sought is vanishingly small relative to the environment in which it must be found — like trying to locate a single needle lost in a large pile of hay; in nanotechnology and biological research the phrase resonates literally: detecting a single molecule of a biomarker in a complex biological fluid, locating a single defect in a large nanofabricated structure, or finding a rare cell type among billions of normal cells are tasks that approach the precision limit of current instruments and methods; advances in nanoscale sensing, single-molecule detection, and machine-learning-assisted image analysis are gradually turning formerly impossible needles-in-haystacks into tractable problems, but the idiom remains a vivid description of the challenge of detection at the limits of resolution and sensitivity

Examples

• Finding a single cancer cell in a blood sample is like finding a needle in a haystack — but liquid biopsy is beginning to make it possible.
• Locating the single defective transistor among billions on a chip is a nanoscale needle-in-haystack problem.