An Integrated Optofluidic Platform Enabling Total Phosphorus On-Chip Digestion and Online Real-Time Detection

Abstract

This paper presents a total phosphorus online real-time monitoring system integrated with on-chip digestion based on the merits of optofluidic technology. The integrated optofluidic device contains a hollow optical fiber employed for pretreatment and digestion of phosphorus solution samples, a polydimethylsiloxane (PDMS)-based micromixer with convergent–divergent walls designed to enable sufficient mixing and chromogenic reaction, and a couple of optical fiber collimators attached with a Z-shaped flow cell for optical detection. Details of system design and fabrication are introduced in this paper. In the experiment, on-chip digestion of four typical phosphates in aqueous solution including organophosphorus and inorganic phosphorus is investigated under different reaction conditions, such as digestion temperature, concentration of oxidant and pH value, and the optimal reaction parameters are explored under different conditions. Meanwhile, we demonstrate the online real-time monitoring function of the optofluidic device, and the digestion mechanisms of four different phosphates are analyzed and discussed. Compared with the national standard method, we find that the measurement accuracy and sensitivity are acceptable when the concentration of total phosphorus is between 0.005–0.9 mg/L (by weight of P) in aqueous solution, which covers the range defined in the national standard. The traditional digestion time of several hours is greatly reduced to less than 10 s, and the content of total phosphorus can be obtained in a few minutes. The integrated optofluidic device can significantly shorten the test time and reduce the sample amount, and also provides a versatile platform for the real-time detection and analysis of many biochemical samples.

Optofluidic Platform for Rapid On-Chip Analysis of Total Phosphorus in Surface Water Using Absorption Spectrometry

“…It was because that the steric hindrance effect of sodium glycerophosphate was lower, and its two hydroxyl hydrogen bonds made the C–O bond disconnected more easily and further promoted the oxidation of phosphate. 21

Figure 3.On-chip digesting the phosphate samples at different flow rates (reaction time). (a) The digestion efficiency as the function of the flow rate (concentration of H 2 O 2 30 mmol/L, pH 3, temperature 30 °C).

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“…It was because that the steric hindrance effect of sodium glycerophosphate was lower, and its two hydroxyl hydrogen bonds made the C-O bond disconnected more easily and further promoted the oxidation of phosphate. 21 To investigate the digestion efficiency of the devices, both a bulk reactor and the microreactor were employed for the digestion, and the reaction rate constant was calculated to judge their efficiency. The digestion reaction rate constant can be calculated by 24…”

“…[17][18][19][20] The digestion reaction at high temperature (>120 °C) and high pressure (1.08-1.37 bar) are essential to convert other valence phosphorus into orthophosphate, and then detect the absorbance of the chromogenic solution by absorption spectrometry. In our previous work, 21 hollow optical fiber was used to build a digestion microreactor to control the temperature of digestion reaction below 90 °C to avoid the impact of gas bubbles on the spectral analysis. However, the pretreatment by heating will still increase the probability of gas bubbles in the device, which will not only reduce the subsequent chromogenic efficiency, but also affect the accuracy of online spectral analysis.…”

Editorial for the Special Issue on IMCO 2019

“…In this Special Issue, 10 papers present integrated, multifunctional physical and chemical sensors based on different platforms such as silicon gas cells [ 1 ], microchips [ 2 , 3 ], and various forms of optical fibers [ 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. These studies well demonstrate the beauty of optofluidics by integrating the microfabricated structures and the micro-optics for high sensitivity and specificity of sensing.…”

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This special issue is a collection of 12 technical papers and two reviews that are expanded into full-length articles from the conference abstracts of the 9th International Multidisciplinary Conference on Optofluidics (IMCO 2019) held in Hong Kong in 14-17 June 2019. The IMCO conference series is held annually to promote scientific exchange and collaboration among leading international researchers across cutting-edge research fields such as micro/nanofluidics, optical devices and systems, plasmonics and metamaterials, biochemical sensors and medical diagnosis, imaging and display, fabrication and integration, and energy and environment.In this Special Issue, 10 papers present integrated, multifunctional physical and chemical sensors based on different platforms such as silicon gas cells [1], microchips [2,3], and various forms of optical fibers [4][5][6][7][8][9][10]. These studies well demonstrate the beauty of optofluidics by integrating the microfabricated structures and the micro-optics for high sensitivity and specificity of sensing.

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