Abstract
Nanoparticle based chemical sensor arrays with four types of organo-functionalized gold nanoparticles (AuNPs) were introduced to classify 35 different teas, including black teas, green teas, and herbal teas. Integrated sensor arrays were made using microfabrication methods including photolithography and lift-off processing. Different types of nanoparticle solutions were drop-cast on separate active regions of each sensor chip. Sensor responses, expressed as the ratio of resistance change to baseline resistance (ΔR/R0), were used as input data to discriminate different aromas by statistical analysis using multivariate techniques and machine learning algorithms. With five-fold cross validation, linear discriminant analysis (LDA) gave 99% accuracy for classification of all 35 teas, and 98% and 100% accuracy for separate datasets of herbal teas, and black and green teas, respectively. We find that classification accuracy improves significantly by using multiple types of nanoparticles compared to single type nanoparticle arrays. The results suggest a promising approach to monitor the freshness and quality of tea products.
Highlights
As one of the most popular beverages, tea is consumed by hundreds of millions of people worldwide [1]
We demonstrated gold nanoparticle based chemiresistor arrays in order to classify
Sensor performance was evaluated based on classification accuracy using linear discriminant analysis (LDA)
Summary
As one of the most popular beverages, tea is consumed by hundreds of millions of people worldwide [1]. Intensive studies have been carried out focusing on sensor performance improvement Functional layers such as amines [23,24,25], biomolecules [26,27], and polymers [28,29] have been reported as capping agents in metal nanoparticle chemiresistors to classify room temperature gases or organic vapors with good accuracy. Sensor electrodes were fabricated using microfabrication methods, and assembled with four types of nanoparticles as the sensing elements, including a pyridine derivative (DMAP, 4-dimethylaminopyridine), a long-chain alkyl amine (ODA, octadecylamine), a bifunctional alkyl thiol (3-MPA, 3-mercaptopropionic acid), and a bifunctional aromatic thiol (4-ATP, 4-aminothiophenol) These monolayer protected AuNPs were chosen based on earlier success in organic vapor sensing [30]. The results demonstrate that nanoparticle-based chemiresistor arrays can be suitable candidates for tea aroma sensing and classification, which may be useful for evaluation of the quality and freshness of tea products
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