Elsevier

Biosensors and Bioelectronics

Volume 67, 15 May 2015, Pages 477-484
Biosensors and Bioelectronics

Paper based platform for colorimetric sensing of dissolved NH3 and CO2

https://doi.org/10.1016/j.bios.2014.09.010Get rights and content

Highlights

  • A low-cost, flexible and reliable method to effectively pattern paper.

  • Target the detection of ammonia (NH3) and carbon dioxide (CO2).

  • Functionalizing the paper platform with diverse cross-reactive dyes sensitive to NH3 and CO2.

  • Selective sensing of NH3 and CO2 and at different concentrations.

  • Flatbed scanner based image capturing and MATLAB® based image processing and analysis.

Abstract

Paper, a cheap and ubiquitous material, has great potential to be used as low-cost, portable and biodegradable platform for chemical and biological sensing application. In this paper, we are exploring a low-cost, flexible and reliable method to effectively pattern paper for capturing optical dyes and for flow-based delivery of target samples for colorimetric chemical sensing. In this paper, we target the detection of ammonia (NH3) and carbon dioxide (CO2), two of the important environmental and health biomarkers. By functionalizing the paper platform with diverse cross-reactive dyes sensitive to NH3 and CO2, their selective sensing within a certain pH range, as well as their detection at different concentrations can be achieved. The images of paper based device were captured by a flatbed scanner and processed in MATLAB® using a RGB model and PCA for quantitative analysis. Paper based devices with readout using ubiquitous consumer electronic devices (e.g. smartphones, flatbed scanner) are considered promising approaches for disease screening in developing countries with limited resources.

Introduction

Paper based microfluidic device has emerged as a new research field and gradually been showing its potential in a variety of applications such as health diagnostics, food quality testing and environmental monitoring (Liana et al., 2012). Paper has several good reasons to be popular: it is a ubiquitous material in our daily life; its cellulose property allows functionalization of different biological and chemical reagents on it (Hossain et al., 2009); meanwhile, liquid can flow through paper's hydrophilic fiber matrix by capillary force without using any external pumps for force; furthermore, the hydrophilicity of paper can be altered by different treatments to create microfluidic channels on paper, resulting in effectively confining and transporting liquid flow in desired manner (Li et al., 2012). Paper-based microfluidic device can be mass produced and easily made into different shapes and thicknesses; therefore they are low-cost, disposable and flexible. These devices, when coupled with readout using ubiquitous commercial electronic devices (e.g. cell phone, PC web camera, flatbed scanner etc.) are considered promising approaches for disease screening in developing countries with limited resources (Martinez et al., 2009).

Considering the merits that paper substrate hold, many exciting developments have been recently reported. Martinez et al. (2008b) have fabricated paper based microfluidic devices by stacking layers of lithography patterned paper and double-sided adhesive paper for glucose and protein measurements. Dungchai et al. (2009) demonstrated electrochemical detection of glucose, lactate and uric acid on paper by adding silver electrodes into the detecting zone on the lithography patterned paper. Although lithography can produce high resolution of microfluidic channels, the disadvantages of this method are that it requires several fabrication steps, it needs different instruments, and it uses several chemicals for development. There are other paper patterning methods such as wax printing (Martinez et al., 2009), inkjet printing (Abe et al., 2008), plasma treatment (Li et al., 2008), and laser treatment (Chitnis et al., 2011). Wax printing was introduced by Whitesides group as a low cost way to create a microfluidic channel on paper. Designed patterns could be printed onto paper by a wax printer and followed by heating to melt the wax (Martinez et al., 2009). However, wax printing still needs a specialized instrument in the form of a wax printer. Laser treatment approach discussed by Chitnis et al. begins with hydrophobic paper and uses laser-based direct writing to pattern hydrophilic regions. Direct writing process is inherently slow and can only be used for low volume manufacturing. Moreover it requires access to high power laser source which may be inaccessible for many in developing regions of the world.

So far, paper based devices have been used for glucose monitoring, protein detection and other applications (Wang et al., 2010, Liana et al., 2012) using variety of biological fluids such as blood, urine etc. Here we present an easy and effective method for hydrophobic–hydrophilic patterning of paper by applying commercially available hydrophobic silicone spray instead of laser or wax treatment, while maintaining low-cost and environmental friendly materials and processing. We also demonstrate the potential of this paper platform for colorimetric sensing of dissolved gas, for example, dissolved CO2 and NH3. NH3 and CO2 are important indicators in health monitoring and disease diagnostics (Tao et al., 2006). No expensive fabrication equipment is required to make these paper based sensing devices. To avoid using bulky and expensive detecting and analyzing methods, optical responses of the dyes on paper were captured by flatbed scanner (Martinez et al., 2008a). The quantitative analysis of the scanned images can be done using MATLAB® where the data can be imported into computer through USB device, Internet or wireless transmission.

Section snippets

Defining and patterning of hydrophilic paper

In this experiment, two types of paper were chosen as the patterning substrate, A4 printing paper and cellulose paper (Whatman cellulose chromatography paper grade 1), both of which are hydrophilic. The hydrophobic patterning agent used here is Atsko Silicone Water-Guard (10.5 oz). The desired pattern was designed in computer and transferred onto paper by printer, followed by hydrophobic patterning. The detailed fabrication procedure is described in Fig. 1.

In Fig. 1(a), desired pattern was

Results and discussion

In the following experiments, hydrophobicity of as-patterned paper platform was tested. The as-patterned paper platform was used for selectively sensing CO2 and NH3. Furthermore, the sensing ability of as-patterned paper platform for detecting dissolved NH3 and CO2 of different concentrations (in the ppm range) was demonstrated. For all the sensing platforms, the RGB information of all the sensing areas was collected and analyzed. Finally, discrimination of the responses of CO2 and NH3 was

Conclusion

In this paper, we showed a new way for patterning paper based devices by using a hydrophobic silicone water repellent spray. This technique is easy, effective and environmentally friendly, and can be considered as one of the cost-effective techniques among others which include wax-printing and inkjet printing. Utilization of commercial electronic products such as a flatbed scanner for RGB optical readout provides a low cost diagnostic platform suitable for resource-poor settings.

It is promising

Acknowledgment

The authors would like to thank Qatar National Research Foundation (QNRF) (PI: Prof. Jong Yoon at Qatar University, Grant no.: NPRP 4-049-2-021) in part for sponsoring time effort for Y.C. to perform this research. We would also like to thank National Science Foundation through its EFRI program (Grant no.: ECCS-1240443) for sponsoring materials and supplies used in this research.

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