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. 2021 Aug 26;12(9):1017.
doi: 10.3390/mi12091017.

Diatom Frustule Array for Flow-Through Enhancement of Fluorescent Signal in a Microfluidic Chip

Zhenhu Wang  1 , De Gong  1 , Jun Cai  1
Affiliations

Diatom Frustule Array for Flow-Through Enhancement of Fluorescent Signal in a Microfluidic Chip

Zhenhu Wang et al. Micromachines (Basel). .

Abstract

Diatom frustules are a type of natural biomaterials that feature regular shape and intricate hierarchical micro/nano structures. They have shown excellent performance in biosensing, yet few studies have been performed on flow-through detection. In this study, diatom frustules were patterned into step-through holes and bonded with silicon substrate to form an open-ended filtration array. Then they were fixed into a microfluidic chip with a smartphone-based POCT. Human IgG and FITC-labeled goat-anti-human IgG were adopted to investigate the adsorption enhancement when analyte flowed through diatom frustules. The results indicated up to 16-fold enhancement of fluorescent signal sensitivity for the flow-through mode compared with flow-over mode, at a low concentration of 10.0 μg/mL. Moreover, the maximum flow rate reached 2.0 μL/s, which resulted in a significant decrease in the testing time in POCT. The adsorption simulation results of diatom array embedded in the microchannel shows good agreement with experimental results, which further proves the filtration enrichment effect of the diatom array. The methods put forward in this study may open a new window for the application of diatom frustules in biosensing platforms.

Keywords: POCT; array; biosensing; diatom frustules; flow-through; microfluidic chip.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The morphology and array of C. sp. frustules. (a) The concave side with evenly distributed ~1 μm pores; (b) The convex side with uniformly distributed ~200 nm and ~40 nm pores; (c) The side view of a diatom frustule indicating the height is about 10 μm; (d) The detailed morphology of the concave side; (e) The detailed morphology of the convex side; (f) The cross section of a diatom frustule, where three layers of pores can be clearly observed. (h) SEM images of the step holes; the diameters are 115 μm and 75 μm, and center distance is 138 μm. The depth of the bigger hole is around 10 μm. (i) Concave-up frustules array and (k) convex-up frustules array, in which each frustule is bonded with the Si substrate by hot-melt glue.
Figure 2
Figure 2
Schematic illustrations of the frustule array modification and detection.
Figure 3
Figure 3
Schematic illustration of (a) POCT devices and (b) microfluidic chip. (c) A picture of the POCT devices.
Figure 4
Figure 4
Pictures of the app interface. (a) Start-up screen; (b) Fluorescence photo capture interface; (c) Photo-processing interface and result output; (d) Binary map of fluorescence photo and distribution chart of fluorescence intensity.
Figure 5
Figure 5
Working principle of the app for fluorescence signal processing.
Figure 6
Figure 6
The average fluorescent intensity of (a) concave-up frustules and (b) convex-up frustules. The fluorescence intensity distribution of 25 frustules of (c) concave-up orientation and (d) convex-up orientation.
Figure 7
Figure 7
Simulation results of concentration distribution of (a) flow-through, (b) flow-over detection, and (c) surface coverage rate of fluorescence molecules over time. (d) Smartphone analysis results of fluorescence intensity of flow-through and flow-over for convex-up frustules.
Figure 8
Figure 8
Simulation results of flow field in single-cell and nanoparticle distribution of cell surface for (a) concave-up frustules, (b) convex-up frustules, and (c) adsorption rate via flow velocity.
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