New approach to a practical quartz crystal microbalance sensor utilizing an inkjet printing system

Online regeneration of a piezoelectric and impedimetric immunosensor for the detection of C-reactive protein on the oriented antibody gold surface

Cardiovascular diseases (CVDs) refer to diseases that affect the heart and blood vessels. CVDs are considered silent killers, which are fatal (death occurs abruptly) particularly when their diagnosis is delayed. Among the biomarkers related to cardiovascular diseases, C-reactive protein (CRP) is expressed or found in high concentrations during a cardiac event. Therefore, CRP is an excellent biomarker to diagnose cardiac events, and therefore quantitative monitoring of CRP is necessary. Herein, we report the fabrication of an immunosensor for the detection and monitoring of CRP. The anti-CRP monoclonal antibody (anti-CRP-mAb), which is specific to the CRP antigen, was immobilized on the surface of gold pre-modified with 4-mercaptophenyl boronic acid (MPBA) to act as a capture antibody. The self-assembled monolayer (SAM) of 4-mercaptophenyl boronic acid (4-MPBA), Au-MPBA, was used for the oriented immobilization of anti-CRP-mAb for piezoelectric (mass-sensitive) and piezoelectric (impedance) measurements. Controlling the orientation of anti-CRP-mAb was crucial to eliminate false positive and negative results during sample analysis. The quartz-crystal microbalance with dissipation (QCM-D) measurements enabled us to follow the covalent immobilization of anti-CRP-mAb on AuCQC-MPBA in real-time. QCM-D was further used to follow the affinity reactions between anti-CRP-mAb and CRP and further with the anti-CRP polyclonal antibody (anti-CRP-pAb). The changes in frequency (Δf, Hz) were related to the changes in the mass (Δm, ng cm^-2) of CRP up to a concentration of 0.10 μg mL^-1, which is equivalent to 0.10 mg L^-1. CRP was detected using the direct affinity immunoassay (anti-CRP-mAb < CRP) and also a sandwich immunoassay using anti-CRP-pAb for signal enhancement. The developed piezoelectric CRP detection protocol was translated to a gold disc electrode for electrochemical impedance spectroscopy (EIS) measurements. The limit of detection (LOD) using both methods was at the μg mL^-1 or mg L^-1 level. Furthermore, the developed electrode could be regenerated using acidic buffer (0.10 M HCl). The detected signal could be reproduced to within 5% relative standard deviation (% RSD) in buffer and serum samples, showing excellent selectivity and specificity toward CRP.

Inkjet Printing and 3D Printing Strategies for Biosensing, Analytical, and Diagnostic Applications

Inkjet printing and 3D inkjet printing have found many applications in the fabrication of a great variety of devices, which have been developed with the aim to improve and simplify the design, fabrication, and performance of sensors and analytical platforms. Here, developments of these printing technologies reported during the last 10 years are reviewed and their versatile applicability for the fabrication of improved sensing platforms and analytical and diagnostic sensor systems is demonstrated. Illustrative examples are reviewed in the context of particular advantages provided by inkjet printing technologies. Next to aspects of device printing and fabrication strategies, the utilization of inkjet dispensing, which can be implemented into common analytical tools utilizing customized inkjet printing equipment as well as state-of-the-art consumer inkjet printing devices, is highlighted. This review aims to providing a comprehensive overview of examples integrating inkjet and 3D inkjet printing technologies into device layout fabrication, dosing, and analytical applications to demonstrate the versatile applicability of these technologies, and furthermore, to inspire the utilization of inkjet printing for future developments.

A Quartz Crystal Microbalance, Which Tracks Four Overtones in Parallel with a Time Resolution of 10 Milliseconds: Application to Inkjet Printing

A quartz crystal microbalance (QCM) is described, which simultaneously determines resonance frequency and bandwidth on four different overtones. The time resolution is 10 milliseconds. This fast, multi-overtone QCM is based on multi-frequency lockin amplification. Synchronous interrogation of overtones is needed, when the sample changes quickly and when information on the sample is to be extracted from the comparison between overtones. The application example is thermal inkjet-printing. At impact, the resonance frequencies change over a time shorter than 10 milliseconds. There is a further increase in the contact area, evidenced by an increasing common prefactor to the shifts in frequency, Δf, and half-bandwidth, ΔΓ. The ratio ΔΓ/(-Δf), which quantifies the energy dissipated per time and unit area, decreases with time. Often, there is a fast initial decrease, lasting for about 100 milliseconds, followed by a slower decrease, persisting over the entire drying time (a few seconds). Fitting the overtone dependence of Δf(n) and ΔΓ(n) with power laws, one finds power-law exponents of about 1/2, characteristic of semi-infinite Newtonian liquids. The power-law exponents corresponding to Δf(n) slightly increase with time. The decrease of ΔΓ/(-Δf) and the increase of the exponents are explained by evaporation and formation of a solid film at the resonator surface.

Impact of Two-Dimensional Particle Size Distribution on Estimation of Water Vapor Diffusivity in Micrometric Size Cellulose Particles

This work aims at assessing the impact of two-dimensional particle size distribution (2D-PSD) on the identification of water vapor diffusivity in micrometric size cellulose particles displaying a size aspect ratio lower than 2 and a cylindrical shape. First, different methodologies to obtain the two-dimensional (2D) particle size distribution (diameter versus length) were compared, based on image analysis. Then, experimental sorption kinetics were obtained by using a quartz crystal microbalance (QCM) coupled with a water vapor adsorption system. Diffusivity values were estimated when considering either the 2D-PSD or global descriptors, such as the mean or median diameter and length of particles. Results revealed that the use of an analytical approach when considering the 2D mean-PSD or the median-PSD was the most accurate way to get diffusivity values at the scale of particles in a polydisperse sample of cellulose particles. Following this approach, a water vapor apparent diffusivity of 3.1 × 10⁻¹² ± 2.3 × 10⁻¹² m²·s⁻¹ was found for the considered cellulose sample. Neglecting PSD in diffusivity estimation led to an underestimation of a factor of 2. This procedure could be extended for all the polydisperse samples in order to have an accurate estimation of water vapor diffusivity at the scale of single particles.

Binding Properties of Split tRNA to the C-terminal Domain of Methionyl-tRNA Synthetase of Nanoarchaeum equitans

The C-terminal domain of methionyl-tRNA synthetase (MetRS-C) from Nanoarchaeum equitans is homologous to a tRNA-binding protein consisting of 111 amino acids (Trbp111) from Aquifex aeolicus. The crystal structure of MetRS-C showed that it existed as a homodimer, and that each monomer possessed an oligonucleotide/oligosaccharide-binding fold (OB-fold). Analysis using a quartz crystal microbalance indicated that MetRS-C freshly isolated from N. equitans was bound to tRNA. However, binding of the split 3'-half tRNA species was stronger than that of the 5'-half species. The T-loop and the 3'-end regions of the split 3'-half tRNA were found to be responsible for the binding. The minimum structure for binding to MetRS-C might be a minihelix-like stem-loop with single-stranded 3'-terminus. After successive duplications of such a small hairpin structure with the assistance of a Trbp-like structure, the interaction of the T-loop region of the 3'-half with a Trbp-like structure could have been evolutionarily replaced by RNA-RNA interactions, along with many combinational tertiary interactions, to form the modern tRNA structure.

Steady State Response Analysis of a Tubular Piezoelectric Print Head

In recent years, inkjet technology has played an important role in industrial materials printing and various sensors fabrication, but the mechanisms of the inkjet print head should be researched more elaborately. The steady state deformation analysis of a tubular piezoelectric print head, which can be classified as a plane strain problem because the radii of the tubes are considerably smaller than the lengths, is discussed in this paper. The geometric structure and the boundary conditions are all axisymmetric, so a one-dimensional mathematical model is constructed. By solving the model, the deformation field and stress field, as well as the electric potential distribution of the piezoelectric tube and glass tube, are obtained. The results show that the deformations are on the nanometer scale, the hoop stress is larger than the radial stress on the whole, and the potential is not linearly distributed along the radial direction. An experiment is designed to validate these computations. A discussion of the effect of the tubes' thicknesses on the system deformation status is provided.