Elsevier

Talanta

Volume 141, 15 August 2015, Pages 188-194
Talanta

Optical paper-based sensor for ascorbic acid quantification using silver nanoparticles

https://doi.org/10.1016/j.talanta.2015.03.067Get rights and content

Highlights

  • Silver nanoparticles used for ascorbic acid quantification in a paper-based sensor.

  • Sensor is portable and requires reduced sample volumes, providing fast analysis.

  • Efficient for several weeks if kept at low temperature and out of light presence.

Abstract

In this paper, we demonstrate for the first time the use of silver nanoparticles (AgNPs) for colorimetric ascorbic acid (AA) quantification in a paper-based sensor. This device is constituted by spot tests modified with AgNPs and silver ions bordered by a hydrophobic barrier which provides quantitative and fast analysis of AA. In addition, this device is employed as point-of-care monitoring using a unique drop of the sample. AgNPs paper-based sensor changed from light yellow to gray color after the addition of AA due to nanoparticle growth and clusters formation. The color intensities were altered as a function of AA concentration which were measured by either a scanner or a homemade portable transmittance colorimeter. Under the selected measurement conditions, results presented limit of detection which was comparable to analytical laboratory-based methodologies. In addition, the sensitivity of our sensor was comparable to the standard titration method when real samples were investigated.

Introduction

Noble metal nanostructures have drawn great interests because of their unique properties based on their surface to volume ratio [1], [2]. Therefore, these materials can be considered as “new” materials that have been increasingly used as biosensors, imaging agents as well as drug delivery vehicles. Recent advances with these materials have allowed the development of robust, highly sensitive and selective detection methods that are envisaged to surpass some limitations of conventional detection procedures [3]. In this context, silver nanoparticles have been considered as promising and powerful tools for sensing and imaging applications due to their optical properties [4], [5], [6], [7], [8], [9], [10], [11], [12], [13].

Thompson et al. used oligonucleotide silver nanoparticle conjugates in a sandwich assay to detect a target oligonucleotide through colorimetric analysis to differentiate a single base mismatch with a lower concentration of a specific DNA sequence [14]. In parallel, a simple but effective method to detect anions (Cl, Br, I, H2PO4, and SCN), in aqueous media, using silver nanoplates, was developed and the sensitivity and selectivity toward inorganic anions showed to be dependent on the surface plasmon resonance band shift [6].

Numerous analyses using metal nanoparticles in aqueous medium are based on the aggregation process. This process forms the basis for a variety of simple, highly sensitive and low cost colorimetric assays [15], [16], [17], [18], [19]. However, the use of silver nanoparticles on a solid substrate, as paper, has not been extensively investigated. Ratnarathorn et al. showed for the first time a modified silver nanoparticles paper-based sensor for Cu2+ colorimetric analysis [20]. In this investigation, AgNPs surface was modified by –COOH and –NH2 functional groups which have strong affinity to Cu2+presence. The sensor was primarily based on the aggregation of modified AgNPs and Cu2+, which leads to a shift in the absorption spectrum [20].

In parallel, ascorbic acid (AA) has been widely used in the pharmaceutical, chemical, cosmetic and food industry as antioxidant [21]. Furthermore, it is naturally present in many fruits and vegetables, like orange, lemon, pineapple, cashew, spinach, and tomato [23]. Specially, orange juice is a commodity broadly traded in the world and Brazil and the United States are the largest producers. It is known that determination of AA is necessary for quality control of different products. The official titrimetric analysis method for AA determination is based on a redox reaction with 2,6-dichloroindophenol (DCIP) [22]. Alternatively, numerous techniques, including chromatographic [23], [24], [25], [26], electrochemical [27], [28], and spectrophotometric techniques [29], [30] have been reported as alternatives for AA determination. However, these analytical methods have the disadvantage of using large volumes of reagents, are time-consuming and the sample preparation induces overestimation or underestimation of AA level. In this context, colorimetric methods are extremely attractive, in particular, for field detection [31]. They can be easily read out by the naked eye, offering advantages of simplicity and rapidity, along with additional cost-effectiveness benefits and no requirements of sophisticated instrumentation [11], [32], [33].

In our study, we describe a point-of-care device using noble nanomaterial for colorimetric ascorbic acid quantification. This sensor uses silver nanoparticles with silver ions as a chromogenic reagent. To the best of our knowledge, there is no report about the use of AgNPs paper-based sensor for AA quantification. The sensor demonstrates an efficient, compact and low-cost platform for quantitative colorimetric analysis in real medicine samples. Sensor color changes result from silver nanoparticles size modifications as well as AgNPs aggregation in response to AA presence.

Section snippets

Materials

All chemicals used in the experiments were of analytical grade and solutions were prepared using high pure water (DI) with a resistivity of 18  cm−1. Silver nitrate (AgNO3), ethylene glycol, ascorbic acid (AA) and polyvinylpyrrolidone (PVP, MW=40,000 g mol−1) were purchased from Sigma-Aldrich. Trisodium citrate and citric acid were obtained from Merck and J. T. Baker, respectively. All glasswares were first rinsed with aqua regia and then thoroughly washed with DI water before use. Paper devices

Performance for the detection of ascorbic acid

Initially, it was investigated whether the interaction of AgNPs and silver ions mixture with vitamin C in a paper-based assay is able to induce a color change and if this change is concentration dependent. Ozyurek et al. obtained quantitative detection of the antioxidant polyphenols in solution based on the reduction of silver ions in the presence of citrate-stabilized silver seeds [40]. This property can be tailored as a result of altering the nanoparticle surface, such as the coating agent

Conclusions

The present work introduces a new optical nanoparticle-based sensor which is devoted to ascorbic acid quantification. The assays are based on the silver nanoparticles growth and clusters formation induced by the ascorbic acid presence. Thus, this platform is a promising alternative for ascorbic acid quantification to the commonly employed dyes. The proposed method provides sufficient sensitivity for one-step measurement of ascorbic acid and is efficient up to three weeks if kept at low

Acknowledgements

Authors would like to thank FAPESP (Project no.: 2011/21954-7) and Brazilian Nanotechnology National Laboratory (LNNano) for all financial support along this work. J.F.A.O. thanks FAPESP for the fellowship granted through the Project 2013/22429-9. We acknowledge LNLS for SAXS measurements and the D1B-SAXS1 beamline staff for all support during experiments.

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    Present address: CTBE – Laboratório Nacional de Ciência e Tecnologia do Bioetanol, Centro Nacional de Pesquisa em Energia e Materiais, CEP 13083-970 Campinas, São Paulo, Brazil.

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