Tsukuru Minamiki

Charged amino acids are the key residues that regulate protein function and stability, and successive sequences of charged amino acids contribute significantly to protein assembly. Therefore, an in-depth understanding of the strengths and manners of amino acid–amino acid interactions (AAIs) caused by successive sequences of charged residues is required. In this study, we prepared self-assembled monolayers (SAMs) bearing charged alkanethiols as ligands to mimic protein surfaces with accumulated charged amino acids. Moreover, we used peptides as analytes to evaluate the AAIs based on chain length. The strengths of the AAIs of tri- and tetrapeptides varied per residue, depending on the properties of the SAMs, such as their densities and hydrophobicities, whereas those of mono- and dipeptides did not vary significantly. Remarkably, the strengths of the AAIs per residue decreased significantly with increasing peptide length, even when the strengths of the AAIs increased at the peptide scale. These results enabled us to quantify the microscopic changes in the AAIs, in addition to the overall interactions governed by the reaction field and alignment of the charged amino acids. Our analysis of AAIs shall be beneficial in protein engineering via genetic mutations based on charged amino acids.

The report on an analytical platform for amino acid–amino acid interactions between charged amino acids and accumulated side chains on self-assembled monolayers combined with field-effect transistors.

Exploring new methodologies for simple and on-demand methods of manipulating the emission and sensing ability of fluorescence sensor devices with solid-state emission molecular systems is important for realizing on-site sensing platforms. In this regard, although conjugated polymers (CPs) are some of the best candidates for preparing molecular sensor devices owing to their luminescent and molecular recognition properties, the development of CP-based sensor devices is still in its early stages. In this study, we herein propose a novel strategy for preparing a chemical stimuli-responsive solid-state emission system based on supramacromolecular assembly-induced emission enhancement (SmAIEE). The system was spontaneously developed by mixing only the component polymers (i.e., polythiophene and a transient cross-linking polymer). The proposed strategy can be applied to the facile preparation of molecular sensor devices. The analyte-induced fluorescent response of polythiophene originated from the dynamic displacement of the transient cross-linker in the polythiophene ensemble and the generation of the polythiophene–analyte complex. Our successful demonstration of the spontaneous preparation of the fluorescence sensor system by mixing two component polymers could lead to the development of on-site molecular analyzers including the determination of multiple analytes.

The development of high-throughput screening methods for microorganisms is desired because microorganisms are useful and sustainable resources with which valuable substances utilized in various industries can be produced. Micro-space-based methods are the best candidates for the efficient screening of microorganisms owing to their low reagent consumption and compact integration. In this study, we developed a picoliter-sized incubator array for quantitative and labeling-free evaluation of the growth process of Escherichia coli (E. coli) by autofluorescence. Because the array with 8464 incubators is able to compartmentalize single E. coli individually utilizing the Poisson distribution, the array can evaluate 100 single E. coli simultaneously. Our incubator array not only realized the high-throughput screening of microorganisms, but also provided an analytical tool for assessing individual differences in E. coli.

This paper reports the development of a real-time monitoring system utilizing the combination of a water-gated organic field-effect transistor (WG-OFET) and a microfluidic chamber for the detection of the herbicide glyphosate (GlyP). For the realization of the real-time sensing with the WG-OFET, the surface of a polymer semiconductor was utilized as a sensing unit. The aqueous solution including the target analyte, which is employed as a gate dielectric of the WG-OFET, flows into a designed microfluidic chamber on the semiconductor layer and the gate electrode. As the sensing mechanism, the WG-OFET-based sensor utilizes the competitive complexation among carboxylate-functionalized polythiophene, a copper(II) (Cu²⁺) ion, and GlyP. The reversible accumulation and desorption of the positively charged Cu²⁺ ion on the semiconductor surface induced a change in the electrical double-layer capacitance (EDLC). The optimization of the microfluidic chamber enables a uniform water flow and contributes to real-time quantitative sensing of GlyP at a micromolar level. Thus, this study would lead to practical real-time sensing in water for various fields including environmental assessment.

Flexible and printed biosensor devices can be used in wearable and disposable sensing systems for the daily management of health conditions. Organic thin-film transistors (OTFTs) are promising candidates for constructing such systems. Moreover, the integration of organic electronic materials and biosensors is of extreme interest owing to their mechanical and chemical features. To this end, the molecular recognition chemistry-based design for the interface between sensor devices and analyte solution is crucial to obtain accurate and reproducible sensing signals of targets, though little consideration has been given to this standpoint in the field of device engineering. Here, we report a printed OTFT on a 1 μm-thick film functionalized with a sensing material. Importantly, the fabricated device quantitatively responds to the addition of a protein immunological marker. These results provide guidelines for the development of effective healthcare tools.

Introduction Glyphosate (GlyP), a widely used herbicide in the agricultural field, was classified as a probable carcinogenic compound (Group 2A) by the International Agency for Research of Cancer (IARS) in 2015. Since then, the importance of the GlyP detection in aqueous media has increased in the field of environmental chemistry and clinical research. The concentration of GlyP in ground and tap water is strictly regulated. For example, the permissible limit for the GlyP concentration in drinking water set at 0.7 ppm in the United States. To-this-date, liquid chromatography (LC) is a common method to sensitively detect GlyP. However, the apparatuses of LC are expensive and require trained personnel, requesting the development of affordable, simple and sensitive sensors for the on-site GlyP detection. Thus, our research has focused on organic field-effect transistors (OFETs) as chemical sensing platforms, because of their low-cost and solution-processability, compact size, and mechanical flexibility[1]. Here, we report an OFET-based chemical sensor for the detection of GlyP in water. Design of the OFET sensor Polythiophene derivatives (PTs) have been widely studied and applied as organic semiconductors in OFET devices. Moreover, PTs has been employed for materials in chemical sensors because their optical and electrical properties can be tuned by introducing artificial receptors into their 3- and/or 4-positions as side chains. However, such OFET-based sensors based on PT attached with artificial receptors are still rare due to the typical high applied voltage (>|20V|) of the OFET which causes materials degradation. Thus we designed a water-gated OFET (WG-OFET) for chemical sensing applications, which could be operated at an ultra-low voltage (<|0.3| V) derived from an electrical double-layer capacitor. For the detection of GlyP, we employed a carboxy side-chain attached to PT (poly{3-(5-carboxypentyl)thiophene-2,5-diyl}, P3CPT) [2] as the semiconductor layer. Due to the molecular wire effect of the π conjugated polymer [3], the sensitive detection of GlyP is expected based on the competitive binding among the carboxylate terminals of P3CPT, copper(II) ions and GlyP in an aqueous solution. Fabrication Method For the fabrication of the WG-OFET sensor device, we applied the side-gate structure (Figure 1). Compared to the conventional multi-stacked OFETs, the planar structure enables easy fabrication process. First, Au electrodes were selected as gate, source and drain, and were deposited on the same substrate. Then, an amorphous perfluoropolymer (Cytop) was used as the hydrophobic bank and patterned with oxygen plasma etching. Finally, a semiconducting polymer P3CPT was deposited onto the channel region by a drop-cast method. In order to prepare the dielectric layer made of aqueous media, 50 µL of 100 mM HEPES (4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid) buffer solution containing 100 mM NaCl was dropped onto the channel region and the gate terminal. After dropping the solution, 40 μM of a copper (II) ion was added into the HEPES buffer solution. The fabricated device was then allowed to stand for 10 minutes to stabilize the transistor characteristics. Results and Conclusions Figure 2 shows the transfer characteristics of the fabricated WG-OFET with the addition of the increasing amount of GlyP from 10 µM to 300 µM in a HEPES buffer solution at pH 7.4 at r.t. As expected, the changes of transfer characteristics were observed by increasing the concentration of GlyP, indicating that the GlyP removed the copper ion from the side-chain of P3CPT. From the low concentration part range of the titration isotherm, the limit of detection (LOD) was estimated to be 0.26 ppm. Notably, the obtained LOD value meets the criteria for the detection of GlyP in drinking water. Furthermore, the selectivity study as shown in Figure 3 demonstrated the highest response of the WG-OFET device to GlyP among the structurally similar carboxylates and phosphates, because of the strong binding affinity of GlyP for copper(Ⅱ) ions. We expect that this study is one step forward in the development of the OFET-based GlyP sensors for environmental and clinical assessment. References [1] R. Kubota, Y. Sasaki, T. Minamiki, T. Minami, Chemical Sensing Platforms Based on Organic Thin-Film Transistors Functionalized with Artificial Receptors, ACS Sens. 4 (2019) 2571–2587. doi:10.1021/acssensors.9b01114 [2] A. Giovannittia, D.T. Sbirceaa, S. Inalb, C. B. Nielsena, E. Bandielloe, D. A. Hanifif, M. Sessoloe, G. G. Malliarasb, I. McCullocha, and J. Rivnay, Controlling the mode of operation of organic transistors through side-chain engineering, Proc. Natl. Acad. Sci. USA. 113 (2016) 12017–12022. doi:10.1073/pnas.1608780113 [3] T. M. Swager, The Molecular Wire Approach to Sensory Signal Amplification, Acc. Chem. Res. 31 (1998) 201–207. doi:10.1021/ar9600502 Figure 1

Invited for the cover of this issue is the group of Tsuyoshi Minami at the University Tokyo. The image illustrates that despite being fabricated with the same polythiophene material, a water‐gated organic thin‐film transistor is a more sensitive device than a fluorescence sensor chip. Read the full text of the article at 10.1002/chem.202003529.