Mathematical modeling of functionalized-microsphere based assays for rapid DNA detection: From sample preparation to results

• We present a model for biomolecule detection by microspheres conjugation.
• The model accounts for sample preparation in a lysis microreactor.
• The model is applied to a diagnostic system based on the HRP enzyme.
• The model provides quantitative estimates regarding the system sensitivity.
• The HRP-based diagnostic is shown to be rapid with very high sensitivity.

Functionalized microspheres are frequently used in the detection of biomolecules. A fundamental understanding of the mechanisms involved in enzymatic assays is required to estimate a method's utility. The mathematical methodology is illustrated through a theoretical analysis to assess the performance of a diagnostic method based on the horseradish peroxidase catalyzed reaction to detect pathogens in clinical specimens. The first part of the analysis focuses on the collection of target DNA molecules onto a functionalized fiber in a lysis micro-reactor (LMR). Expressions are derived for hybridization rates that include convective transport. In the next step the fiber is contacted with functionalized chitosan microspheres containing horse radish peroxidase. Chitosan microspheres are conjugated to the fiber with the target DNA acting as a unique tether. The final step is the release of chitosan microspheres in a chromogenic substrate and monitoring absorption changes. The analysis provides estimates of the method sensitivity and processing time and we show that DNA with a concentration as low as 10−4 copies per milliliter can be detected in less than 30 min. The modeling methodology presented can readily be extended to similar enzymatic, microsphere-based assays for quantitative purposes and feasibility studies.

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