A Simple Metallothionein-Based Biosensor for Enhanced Detection of Arsenic and Mercury

Abstract

Metallothioneins (MTs) are a family of cysteine-rich proteins whose biological roles include the regulation of essential metal ions and protection against the harmful effects of toxic metals. Due to its high affinity for many toxic, soft metals, recombinant human MT isoform 1a was incorporated into an electrochemical-based biosensor for the detection of As3+ and Hg2+. A simple design was chosen to maximize its potential in environmental monitoring and MT was physically adsorbed onto paper discs placed on screen-printed carbon electrodes (SPCEs). This system was tested with concentrations of arsenic and mercury typical of contaminated water sources ranging from 5 to 1000 ppb. The analytical performance of the MT-adsorbed paper discs on SPCEs demonstrated a greater than three-fold signal enhancement and a lower detection limit compared to blank SPCEs, 13 ppb for As3+ and 45 ppb for Hg2+. While not being as low as some of the recommended drinking water limits, the sensitivity of the simple MT-biosensor would be potentially useful in monitoring of areas of concern with a known contamination problem. This paper describes the ability of the metal binding protein metallothionein to enhance the effectiveness of a simple, low-cost electrochemical sensor.

Paper-Based Biosensors for Analysis of Water

“…There are different types of paper that are used for fabrication of paper-based devices ( Table 1). Filter papers have been widely used as substrate material to paper-based devices for biosensor application [16][17][18][19]. There are a vast range of commercially available high-quality filter papers, mainly constituted of alpha cellulose, a highly stable form of cellulose.…”

“…The filter paper grade 1, considered as a medium retention and flow filter paper, has been functionalized to obtain paper-based immunosensors [16,17]. Irvine et al adsorbed metallothioneins in grade 1 filter paper for the detection of heavy metals [18]. In the same way, other filter paper grades have been used, such as the slow filter paper grade 42 (pore size of 2.5 μm) for the incorporation of an in vitro transcription/translation system [19].…”

“…For example, Rengaraj et al [27] fabricated a paper-based electrode by printing three layers of a carbon-based conductive ink onto hydrophobic printer paper. Other fabrication techniques include a simple procedure of cutting by punching [18,19], obtaining discs with millimetric dimensions that can be functionalized and/or introduced into devices, such as commercial screen-printed electrodes [18].…”

“…The electrochemical paper-based biosensors are based on the modification of paperbased platforms placed in commercial screen-printed electrodes [17,18], or rely on the fabrication of lab-made functionalized paper-based screen-printed electrodes [27].…”

“…A complex comprising magnetic beads, gold nanoparticles (AuNPs), and the functional nucleotide GR5-DNAzyme was applied as a biorecognition element of lead ion [20]. In another work, the recombinant human metallothionein 1a, a metal-binding protein [18], was used for the recognition of As 3+ and Hg 2+ in water. The tetrameric protein lectin concanavalin A (obtained from Canavalia ensiformis), selective to carbohydrates on bacterial cells, was selected as a biorecognition element of bacterial cultures from sewage sludge [27].…”