Clamped-end effect on static detection signals of DNA-microcantilever

Boundary constraint induced inhomogeneous effects are important for mechanical responses of nano/micro-devices. For microcantilever sensors, the clamped-end constraint induced inhomogeneous effect of static deformation, so called the clamped-end effect, has great influence on the detection signals. This paper is devoted to developing an alternative mechanical model to characterize the clamped-end effect on the static detection signals of the DNA-microcantilever. Different from the previous concentrated load models, the DNA adsorption is taken as an equivalent uniformly distributed tangential load on the substrate upper surface, which exactly satisfies the zero force boundary condition at the free-end. Thereout, a variable coefficient differential governing equation describing the non-uniform deformation of the DNA-microcantilever induced by the clamped-end constraint is established by using the principle of minimum potential energy. By reducing the order of the governing equation, the analytical solutions of the curvature distribution and static bending deflection are obtained. By comparing with the previous approximate surface stress models, the clamped-end effect on the static deflection signals is discussed, and the importance of the neutral axis shift effect is also illustrated for the asymmetric laminated microcantilever.

Rapid and Sensitive Detection of Severe Acute Respiratory Syndrome Coronavirus 2 in Label-Free Manner Using Micromechanical Sensors

Coronavirus (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been identified as a deadly pandemic. The genomic analysis of SARS-CoV-2 is performed using a reverse transcription-polymerase chain reaction (RT-PCR) technique for identifying viral ribonucleic acid (RNA) in infected patients. However, the RT-PCR diagnostic technique is manually laborious and expensive; therefore, it is not readily accessible in every laboratory. Methodological simplification is crucial to combat the ongoing pandemic by introducing quick, efficient, and affordable diagnostic methods. Here, we report how microcantilever sensors offer promising opportunities for rapid COVID-19 detection. Our first attempt was to capture the single-stranded complementary DNA of SARS-CoV-2 through DNA hybridization. Therefore, the microcantilever surface was immobilized with an oligonucleotide probe and detected using complementary target DNA hybridization by a shift in microcantilever resonance frequency. Our results show that microcantilever sensors can discriminate between complementary and noncomplementary target DNA on a micro to nanoscale. Additionally, the microcantilever sensors’ aptitude toward partial complementary DNA determines their potential to identify new variants of coronavirus. Therefore, microcantilever sensing could be a vital tool in the effort to extinguish the spreading COVID-19 pandemic.

Development of calix[4]arenes modified at their narrow- and wider-rims as potential metal ions sensor layers for microcantilever sensors: further studies

The development of a microcantilever (MCL) sensing device capable of simultaneously detecting several metal ionic species in aqueous media with low limits of detection requires a variety of sensing layers which are ion-specific. Calix[4]arenes are robust molecules which can be easily modified and have been extensively studied for their ion binding properties. They are also capable of forming self-assembled monolayers (SAMs) onto the gold layers of MCLs and are capable of detecting various metal ions with different anionic counterions in aqueous solutions. In this paper we report on the effect of the alkoxy group in the narrow rim [O-(alkoxycarbonyl)methoxy] substituents of bimodal calix[4]arenes which have been used as metal ion MCL sensing layers, using classical solution state experimental studies. A DFT computational study to compare the experimental results with several metal ions is also reported herein.

A Numerical Model of a Perforated Microcantilever Covered with Cardiomyocytes to Improve the Performance of the Microcantilever Sensor

A few simple polymeric microsystems, such as microcantilever sensors, have recently been developed for the preliminary screening of cardiac toxicity. The microcantilever deflection produced by a change in the cardiomyocyte (CM) contraction force is important for understanding the mechanism of heart failure. In this study, a new numerical model is proposed to analyze the contractile behavior of CMs cultured on a perforated microcantilever surface for improving the performance of the microcantilever sensor. First, the surface traction model is used to investigate the bending displacement of the plain microcantilever. In order to improve the bending effect, a new numerical model is developed to analyze the bending behavior of the perforated microcantilever covered with CMs. Compared with the designed molds, the latter yields better results. Finally, a simulation analysis is proposed based on a finite element method to verify the presence of a preformed mold. Moreover, the effects of various factors on the bending displacement, including microcantilever size, Young’s modulus, and porosity factor, are investigated. Both the simulation and numerical results have good consistency, and the maximum error between the numerical and simulation results is not more than 3.4%, even though the porosity factor reaches 0.147. The results show that the developed mold opens new avenues for CM microcantilever sensors to detect cardiac toxicity.

Silicon Microcantilever Sensors to Detect the Reversible Conformational Change of a Molecular Switch, Spiropyan

The high sensitivity of silicon microcantilever sensors has expanded their use in areas ranging from gas sensing to bio-medical applications. Photochromic molecules also represent promising candidates for a large variety of sensing applications. In this work, the operating principles of these two sensing methods are combined in order to detect the reversible conformational change of a molecular switch, spiropyran. Thus, arrays of silicon microcantilever sensors were functionalized with spiropyran on the gold covered side and used as test microcantilevers. The microcantilever deflection response was observed, in five sequential cycles, as the transition from the spiropyran (SP) (CLOSED) to the merocyanine (MC) (OPEN) state and vice-versa when induced by UV and white light LED sources, respectively, proving the reversibility capabilities of this type of sensor. The microcantilever deflection direction was observed to be in one direction when changing to the MC state and in the opposite direction when changing back to the SP state. A tensile stress was induced in the microcantilever when the SP to MC transition took place, while a compressive stress was observed for the reverse transition. These different type of stresses are believed to be related to the spatial conformational changes induced in the photochromic molecule upon photo-isomerisation.

Double side nanostructuring of microcantilever sensors with TiO2-NTs as a route to enhance their sensitivity

A double side nanostructured microcantilever with ordered, aligned and open TiO2 nanotubes.

Cantilever-Droplet-Based Sensing of Magnetic Particle Concentrations in Liquids

Cantilever-based sensors have attracted considerable attention in the recent past due to their enormous and endless potential and possibilities coupled with their dynamic and unprecedented sensitivity in sensing applications. In this paper, we present a technique that involves depositing and vaporizing (at ambient conditions) a particle-laden water droplet onto a defined sensing area on in-house fabricated and commercial-based silicon microcantilever sensors. This process entailed the optimization of dispensing pressure and time to generate and realize a small water droplet volume (Vd = 49.7 ± 1.9 pL). Moreover, we monitored the water evaporation trends on the sensing surface and observed total evaporation time per droplet of 39.0 ± 1.8 s against a theoretically determined value of about 37.14 s. By using monodispersed particles in water, i.e., magnetic polystyrene particles (MPS) and polymethyl methacrylate (PMMA), and adsorbing them on a dynamic cantilever sensor, the mass and number of these particles were measured and determined comparatively using resonant frequency response measurements and SEM particle count analysis, respectively. As a result, we observed and reported monolayer particles assembled on the sensor with the lowest MPS particles count of about 19 ± 2.

THE APPLICATION PROSPECT OF MICROCANTILEVER SENSORS TECHNOLOGY ON MINERAL SURFACE ADSORPTION

The main purpose of this review is to present a new method to study the adsorption mechanism of reagents on mineral surfaces based on a microcantilever sensor system. The mechanisms of micro/nanoscale adsorption are of great significance in the interface sorting of minerals in the field of mineral processing. The sensing technique based on a microcantilever has become attractive with the advantages of label-free detection, high sensitivity, high-throughput, and fast response time. This review first discusses the structure, working principle, working modes, detection methods, and reported applications of microcantilever sensors. When combined with the working principle and applications, microcantilever sensors can monitor the adsorption process of reagents on mineral surfaces in real time. In the second part of this review, we will discuss the potential applications of microcantilever sensors in the interfacial adsorption of minerals.