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Open AccessArticle

Micro-Droplet Detection Method for Measuring the Concentration of Alkaline Phosphatase-Labeled Nanoparticles in Fluorescence Microscopy

1
School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
2
Emory University School of Medicine, Georgia Institute of Technology, Atlanta, GA 30329 USA
*
Author to whom correspondence should be addressed.
Sensors 2017, 17(11), 2685; https://doi.org/10.3390/s17112685
Received: 1 October 2017 / Revised: 17 November 2017 / Accepted: 19 November 2017 / Published: 21 November 2017
This paper developed and evaluated a quantitative image analysis method to measure the concentration of the nanoparticles on which alkaline phosphatase (AP) was immobilized. These AP-labeled nanoparticles are widely used as signal markers for tagging biomolecules at nanometer and sub-nanometer scales. The AP-labeled nanoparticle concentration measurement can then be directly used to quantitatively analyze the biomolecular concentration. Micro-droplets are mono-dispersed micro-reactors that can be used to encapsulate and detect AP-labeled nanoparticles. Micro-droplets include both empty micro-droplets and fluorescent micro-droplets, while fluorescent micro-droplets are generated from the fluorescence reaction between the APs adhering to a single nanoparticle and corresponding fluorogenic substrates within droplets. By detecting micro-droplets and calculating the proportion of fluorescent micro-droplets to the overall micro-droplets, we can calculate the AP-labeled nanoparticle concentration. The proposed micro-droplet detection method includes the following steps: (1) Gaussian filtering to remove the noise of overall fluorescent targets, (2) a contrast-limited, adaptive histogram equalization processing to enhance the contrast of weakly luminescent micro-droplets, (3) an red maximizing inter-class variance thresholding method (OTSU) to segment the enhanced image for getting the binary map of the overall micro-droplets, (4) a circular Hough transform (CHT) method to detect overall micro-droplets and (5) an intensity-mean-based thresholding segmentation method to extract the fluorescent micro-droplets. The experimental results of fluorescent micro-droplet images show that the average accuracy of our micro-droplet detection method is 0.9586; the average true positive rate is 0.9502; and the average false positive rate is 0.0073. The detection method can be successfully applied to measure AP-labeled nanoparticle concentration in fluorescence microscopy. View Full-Text
Keywords: fluorescence microscopy; micro-droplet; spot detection; alkaline phosphatase (AP); nanoparticles fluorescence microscopy; micro-droplet; spot detection; alkaline phosphatase (AP); nanoparticles
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MDPI and ACS Style

Li, R.; Wang, Y.; Xu, H.; Fei, B.; Qin, B. Micro-Droplet Detection Method for Measuring the Concentration of Alkaline Phosphatase-Labeled Nanoparticles in Fluorescence Microscopy. Sensors 2017, 17, 2685. https://doi.org/10.3390/s17112685

AMA Style

Li R, Wang Y, Xu H, Fei B, Qin B. Micro-Droplet Detection Method for Measuring the Concentration of Alkaline Phosphatase-Labeled Nanoparticles in Fluorescence Microscopy. Sensors. 2017; 17(11):2685. https://doi.org/10.3390/s17112685

Chicago/Turabian Style

Li, Rufeng; Wang, Yibei; Xu, Hong; Fei, Baowei; Qin, Binjie. 2017. "Micro-Droplet Detection Method for Measuring the Concentration of Alkaline Phosphatase-Labeled Nanoparticles in Fluorescence Microscopy" Sensors 17, no. 11: 2685. https://doi.org/10.3390/s17112685

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