Limitation of this study is that

Limitation of this study is that only healthy individuals were included so that there were no extreme high/low Epigenetics Compound Library values detected. The study of the relationship between blood glucose and salivary glucose based on age, gender, medical, and health conditions is highly needed. These outcomes would improve statistical confidence by increasing the study population. The sensor is designed to measure as low as 0.1mg/dL and as high as 20mg/dL glucose in saliva, which is sufficient to be medically applicable for diabetic diagnosis and health surveillance.
Conflict of interest
Acknowledgements Our research work was conducted at the Gorge J. Kostas Nanoscale Technology and Manufacturing Research Center at Northeastern University, and we would like to thank for the fund from NanoBio Systems LLC (NBS) under Grant No. 0731102.
Introduction S-Nitros(yl)ation is a reversible modification of free cysteine residues mediated by nitric oxide (NO), resulting in generation of S-nitrosothiols. NO can react with thiol group of cysteine residues to form S-nitrosothiols (S-nitrosylation) [1,2]. S-Nitrosylation was thought to be controlled principally through the regulation of NO biosynthesis. Emerging evidences, however, indicate that nitrosothiol (SNO) turnover may provide an alternative regulatory mechanism [3,4]. S-Nitrosylation of the antioxidant tripeptide glutathione forms S-nitrosoglutathione (GSNO), which is thought to function as a mobile reservoir of NO bioactivity [5]. During the past few years, S-nitrosylation, the covalent and reversible binding of NO to the thiols of reduced reactive cysteine residues, has emerged as an important posttranslational modification [6]. S-Nitrosylation is thought to account for much of the widespread influence of NO on cellular signaling through redox-based biochemical regulation of signaling component [7,8]). Protein S-nitrosylation can produce a labile S-nitrosothiol structure and some functional alterations, containing a broad range of physiological and pathological cellular instances [9,10]. There are some techniques to detect S-nitrosylated protein, including UV–Vis spectroscopy [11], electrochemistry [12,13], Biotin switch method [14], high performance liquid chromatography–tandem mass spectroscopy (HPLC–MS) [15,16], Gold nanoparticle enrichment technique [17] and fluorescence labeling method [18]. However, these methods for detection S-nitrosylated protein seem to be insufficient. The method of UV–Vis spectroscopy is simple, but has many disturbing components. There are a lot of advantages of electrochemical method to monitor S-nitrosylation, which can obtain higher sensitivity, accuracy and wider measuring range compared to other methods. However, many disadvantages, such as long time and poor repeatability, make it significantly more difficult to perform. Biotin switch method is relatively effective and sensitive, but this method may produce false negative results. Fluorescein labeling method has the advantage of saving time, can qualitatively analyze single pure but not mixture samples, and fails to determine the site of S-nitrosylation. Surface plasmon resonance (SPR), a surface-sensitive detecting technique based on changes in refractive index (RI), can be used to measure the changes occurring on the thin metal films as a result of recognition events or chemical reactions [19,20]. Owing to its features of simplicity, low cost, non-labeling, high-sensitivity and real-time measurement, SPR monitoring has received much interest from scientific community [21–24]. This interesting technique has become a widely method used to monitor protein binding, drug screening, environmental contaminants and biochemical reactions [25–28]. In this paper, a simpler and more selective method for detection S-nitrosylated proteins by using SPR technology were established and successfully applied to analyze the protein S-nitrosylation in peach fruit.
Material and methods