# Protein biomarker discovery in neural tissue: a comparative analysis of immunoassay and colloidal gold lateral flow assay method

## TL;DR

This study compares two methods for detecting a protein in nerve tissue, finding that one is much more sensitive and accurate.

## Contribution

The study provides a direct comparison of ELISA and colloidal gold lateral flow assays for AChE detection in formalin-fixed neural tissue.

## Key findings

- ELISA detected AChE in all samples with concentrations as low as 0.5 ng/mL, while colloidal gold only detected samples above 10–20 ng/mL.
- Colloidal gold assays showed poor quantitative agreement and higher variability compared to ELISA.
- The strip test may be suitable for rapid detection of high-abundance biomarkers but lacks sensitivity for low-level diagnostics.

## Abstract

Sensitive detection of protein biomarkers in neural tissue is important for both research and diagnostic applications. Enzyme-linked immunosorbent assay (ELISA) is a gold-standard immunoassay known for high sensitivity and quantification, whereas colloidal gold lateral flow assays offer rapid, instrument-free testing but are generally qualitative. This study compared ELISA and colloidal gold strip tests for detecting acetylcholinesterase (AChE) in formalin-fixed cadaveric nerve tissues. Five cadavers (3 males, 2 females) without neurological disease or limb trauma provided proximal and distal nerve segments for analysis. Tissues were formalin-fixed, heat-treated to reverse cross-links, and extracted for protein. A bicinchoninic acid (BCA) assay measured total protein yields, and an ELISA quantified AChE concentration. In parallel, a colloidal gold immunochromatographic strip test was applied to diluted extracts to visually detect AChE.

We evaluated detection sensitivity (limit of detection and positive detection rate), reproducibility (intra-assay variability), and quantitative agreement between methods.

ELISA detected AChE in 12/12 extracted nerve samples, with concentrations ranging from ~0.2 to 66 ng/mL in tissue extract (mean ~15 ng/mL). The colloidal gold strips, by contrast, returned visible positive lines only for samples above ~10–20 ng/mL AChE; low-level samples yielded no signal. ELISA showed a lower limit of detection around 0.5 ng/mL, approximately one order of magnitude lower than the strip test. ELISA measurements were highly reproducible (the duplicate-well coefficient of variation ~10–15%), whereas the lateral flow results were more variable near the cutoff and required subjective interpretation of faint test lines. A strong rank correlation (ρ ≈ 0.9) was found between ELISA concentrations and strip test positivity thresholds. However, Bland–Altman analysis revealed the strip method systematically under-reported AChE levels, highlighting poor quantitative agreement.

The ELISA demonstrated superior sensitivity and accuracy for AChE in formalin-fixed neural tissue extracts, detecting low concentrations that the colloidal gold lateral flow assay missed. While the rapid strip test may be useful for quick yes/no identification of high-abundance biomarkers in nerve samples, it lacks the sensitivity and quantitative precision necessary for reliable neural protein diagnostics. Integration of more sensitive detection labels or reader devices would be required to bridge the performance gap between lateral flow assays and ELISA in this context.

Diagram comparing AChE detection sensitivity between two methods. On the left, ELISA shows a lower limit of detection at 0.5 nanograms per milliliter. On the right, Colloidal Gold has a lower limit of detection between 10 and 20 nanograms per milliliter.