Elsevier

Biosensors and Bioelectronics

Volume 174, 15 February 2021, 112804
Biosensors and Bioelectronics

Real-time monitoring of geosmin based on an aptamer-conjugated graphene field-effect transistor

https://doi.org/10.1016/j.bios.2020.112804Get rights and content

Highlights

  • Water supply system suffers serious issues with odor compounds annually.

  • Nanobiosensors to detect target molecule sensitively are needed.

  • Nanomaterials were modified with target specific reactive aptamer.

  • Real-time monitoring with graphene electronics showed high sensitivity and accuracy using river water sample.

Abstract

In this paper, we propose a novel field-effect transistor (FET) using graphene, which is a two-dimensional (2D) nanomaterial, capable of evaluating water quality, and immobilizing the surface of a graphene micropatterned transistor with a highly responsive bioprobe for a water contamination indicator, geosmin, with high selectivity. A high-quality bioprobe-immobilized graphene FET (GFET) was fabricated for the real-time monitoring of geosmin using a liquid-gate measurement configuration. Immobilization was confirmed by measuring the change in the electrical characteristics of the platform (slope of the current-voltage (I–V) curve) and fluorescence images. In addition, a selectivity test showed remarkable implementation of the highly sensitive sensing platform with an insignificant signal when a nontarget was added. Using the fabricated device, the linear range for geosmin detection was determined to be from 0.01 nM - 1 μM with a detection limit of 0.01 nM. In addition, geosmin concentrations as low as 10 nM could be determined from river water samples with the sensor platform. This sensor can be utilized to immediately determine the presence of odorous substances by analyzing a water supply source without additional pretreatment. Another advantage is that the sensor device is a promising tool that does not have special equipment that requirs careful maintenance. In addition, the device provides a new platform for detecting harmful substances in various water sources by varying the bioprobes that are empolyed.

Introduction

As the Earth is becoming warmer, severe environmental issues, such as increases in the temperatures of seawater and reservoirs, persistent drought and sharply rising desert areas, have become urgent problems. In particular, continuous climate change makes drinkable water useless due to blooms of algae such as diatoms, green algae and blue-green algae (cyanobacteria) (Suurnakki et al., 2015; Urase and Sasaki, 2013). Geosmin, which has a musty odor, is an algae metabolite that contaminates water supply systems. As shown by several research results, one of the main reasons for the low satisfaction levels of tap water is odor compounds (Watson et al., 2016; Parinet et al., 2010), which remain after flowing through the water supply system. To increase trust and satisfaction with drinking water, the sensitive detection of odor compounds below the concentrations detectable by the human nose is critical (Xu et al., 2020). The human sense of smell is very sensitive and can detect at least 5 ppt geosmin. The detection of minute concentrations of geosmin or other metabolites from algae is necessary. However, detecting geosmin at low concentrations has been challenging for existing instruments. In addition, existing devices show limitations in the real-time monitoring of algae because pretreatment is time-consuming, and an expert is required to operate the necessary equipment.

Various sensing platforms have been developed for the detection of odor compounds that are contained in water and for monitoring water quality (Lvova et al., 2020; Braga et al., 2012; Migliorini et al., 2020; Hurlburt et al., 2009; Ji et al., 1999; Kim et al., 2015), such as gas chromatography-mass spectrometry (GC-MS), headspace-solid-phase microextraction (HS-SPME) (Parinet et al., 2011), and gas chromatography-flame ionization detection (GC-FID) (Bristow et al., 2019) (Table S1). These conventional detection methods cannot cope with rapid and sensitive sensing. Although the current state-of-the-art analysis methods can detect geosmin, they have a few limitations, such as high cost, a long and complex pretreatment system, the need for a large sample volume to obtain sufficient sensitivity (Bristow et al., 2019), and large equipment. In addition, conventional instrumentation requires skillful equipment operators. To overcome these limitations, researchers are inventing new methodologies (Xu et al., 2018; Guo, 2017, Guo, 2018; Guo and Ma, 2017; Guo et al., 2018).

The bioelectronic nose, which is based on a carbon nanotube (CNT) sensor platform that is integrated with mammalian cell-derived nanovesicles for geosmin detection, has been demonstrated (Son et al., 2015). In this work, a human olfactory receptor (hOR) binding geosmin with high selectivity was screened by a cell-based assay and utilized as a recognition element in the form of a nanovesicle. However, for practical application, the nanovesicle-based bioelectronic nose has several limitations including low stability and high cost. Our research focused on the highly sensitive and selective detection of geosmin with a graphene field-effect transistor (GFET) using a target-specific aptamer to obtain the advantages of FET-based sensors, such as a fast response, high sensitivity and selectivity with target-specific bioprobes, and low cost (Park et al., 2016). Graphene is the most promising chemical and biosensor material; it shows extremely high electrical conductivity (200,000 cm2 V-1 s-1) and ambipolar transfer characteristics (Wang et al., 2020). The GFET platform has numerous advantages as an electrochemical sensor, such as excellent sensitivity, real-time monitoring, rapid responses, and exceedingly selective responses (Park et al., 2017). Therefore, these systems have been employed for a wide range of applications, including the detection of bacteria, viruses, etc (Yang et al., 2014). Aptamers can be isolated by an in vitro selection process and have attracted considerable attention as a bioprobe because of their high stability and reproducibility, easy modification and immobilization, and small size. Recently, in many studies, aptamers that are incorporated into FET platforms have shown high performance in terms of selectivity and sensitivity. However, isolation and integration of aptamers that can recognize geosmin with a GFET have not been reported.

In this paper, we demonstrate a device that is based on a novel isolated-aptamer-conjugated GFET platform and enables that allows for the selective detection of geosmin (Scheme 1). The device consists of a source, drain and gate. The gate modulator showed excellent performance because the minimum detection level (MDL) for geosmin was approximately 10 pM. We proposed a real-time monitoring sensor that showed high-performance detection in real water samples. The whole detection process can be completed within 30 min. With geosmin-containing river water, real-time monitoring and a comparison of experimental results between GC/MS and the GFET-based sensor were conducted successfully. The performance suggested the possibility of using the device in real-time water monitoring. Our technique can be applied for the detection of various targets. A sensor technology that is capable of real-time detection of algae in the field rather than the laboratory is required. The micropatterned graphene-based transistor is a promising approach for meeting the demand as a water contamination sensor platform. In addition, due to increasing eutrophication, the amount of odorous substances is expected to increase in the future.

Section snippets

Materials

All chemicals and reagents were of analytical grade and utilized as received: 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM), 2-methylisoborneol (MIB), 2-Isopropyl-3-methoxypyrazine (IPMP) and 2-Isobutyl-3-methoxypyrazine (IBMP) were purchased from Sigma Aldrich. Geosmin aptamer with 5′-end amine groups (5′-NH2-CCC CCC-GGG ACG ACC CGT TTG TTC CTC GGC TTT TTA AGA GGT CTG GTT GAT–3′) was purchased from BIONEER. Poly(methyl methacrylate), 950 PMMA A4 4% in anisole, was

Fabrication of the GFET platform

Wafer-scale graphene was synthesized via the CVD method by repeating the preannealing, growth and cooling processes. A schematic of the procedure and specific regulating factors of each step is presented in Fig. 1a. The fabricated graphene was transferred onto a silicon wafer for further operation. Successful products were confirmed by analyzing TEM images of graphene loaded on TEM grid (Fig. 1b). In addition, via Raman spectral analysis, the characteristics of the graphene layer were verified.

Conclusions

In this work, the overall research objective was to evaluate a micropatterned graphene-loaded FET sensor for the detection of geosmin, which is an odorous algae metabolite. For the evaluation, graphene was fabricated to act as a transistor on the electrode. The outstanding performance of the sensor was confirmed by the sensitive detection of geosmin under 0.01 nM. The proposed sensor platform showed reasonable sensitivity for target analytes, and the detection limit for geosmin was lower than

CRediT authorship contribution statement

Seon Joo Park: Methodology, Validation, Writing - review & editing, Data curation, Data Curation. Sung Eun Seo: Methodology, Validation, Writing - review & editing, Data curation, Data Curation. Kyung Ho Kim: Formal analysis. Sang Hun Lee: Resources, Formal analysis. Jinyeong Kim: Resources, Formal analysis. Siyoung Ha: Methodology. Hyun Seok Song: Conceptualization, Investigation. Seung Hwan Lee: Writing - review & editing, Data curation, Investigation. Oh Seok Kwon: Writing - review &

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry (IPET) through the Advanced Production Technology Development Program, funded by the Ministry of Agriculture, Food and Rural Affairs(MAFRA) (318104-3); the “Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ014790022020)” Rural Development Administration, Republic of Korea; the National Research Foundation of Korea (NRF) Grant

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    These authors contributed equally to this work.

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