Superhydrophobic Paper-Based Microfluidic Field-Effect Transistor Biosensor Functionalized with Semiconducting Single-Walled Carbon Nanotube and DNAzyme for Hypocalcemia Diagnosis

Hypocalcemia is caused by a sharp decline in blood calcium concentration after dairy cow calving, which can lead to various diseases or even death. It is necessary to develop an inexpensive, easy-to-operate, reliable sensor to diagnose hypocalcemia. The cellulose-paper-based microfluidic field-effect biosensor is promising for point-of-care, but it has poor mechanical strength and a short service life after exposure to an aqueous solution. Octadecyltrichlorosilane (OTS), as a popular organosilane derivative, can improve the hydrophobicity of cellulose paper to overcome the shortage of cellulose paper. In this work, OTS was used to produce the superhydrophobic cellulose paper that enhances the mechanical strength and short service life of MFB, and a microfluidic field-effect biosensor (MFB) with semiconducting single-walled carbon nanotubes (SWNTs) and DNAzyme was then developed for the Ca²⁺ determination. Pyrene carboxylic acid (PCA) attached to SWNTs through a non-covalent π-π stacking interaction provided a carboxyl group that can bond with an amino group of DNAzyme. Two DNAzymes with different sensitivities were designed by changing the sequence length and cleavage site, which were functionalized with SPFET/SWNTs-PCA to form Dual-MFB, decreasing the interference of impurities in cow blood. After optimizing the detecting parameters, Dual-MFB could determine the Ca²⁺ concentration in the range of 25 μM to 5 mM, with a detection limit of 10.7 μM. The proposed Dual-MFB was applied to measure Ca²⁺ concentration in cow blood, which provided a new method to diagnose hypocalcemia after dairy cow calving.     

多壁碳纳米管在不同表面功能基团自组装膜上的沉积

制备了表面功能基团为氨基和甲基的自组装膜,将不同表面功能基团自组装膜浸入多壁碳纳米管分散液中沉积,实验观察到,表面为氨基的APTES自组装膜对分散液中的碳纳米管有静电吸附作用而均匀吸附一层碳纳米管,表面为甲基的OTS自组装膜对分散液碳纳米管有排斥作用力而没有吸附碳纳米管,这一实验对利用单根碳纳米管构造纳米电子器件与纳米机械具有重要意义。     

AFM measurements of hydrophobic forces between a polyethylene sphere and silanated silica plates- the significance of surface roughness

Recently, substantial research effort has been devoted to the study of non-DLVO forces between hydrophobic surfaces. However, the significance of surface roughness in the analysis of these hydrophobic attractive forces has not been given sufficient consideration and research is now in progress to attend to this issue. Fused silica plates covered with adsorbed octadecyltrichlorosilane (OTS) were characterized by water contact angle measurements and atomic force microscopy (AFM). Surfaces with different surface coverages and different contact angles were obtained by variation of the adsorption time. OTS formed patches on the silica surfaces, the lateral size and height of which depended on the adsorption time. Such surfaces exhibit differences in roughness at the sub-nanometer level. Using the AFM colloidal probe technique, forces between a polyethylene sphere and silanated silica surfaces were measured in water. Long-range attractive forces were found, usually referred to as hydrophobic forces. The resulting force vs. distance curves were fitted with a double exponential function. The magnitude of the short-range part of the force curves seems to correlate with water contact angles at silanated silica surfaces. On the other hand, the range of the long-range force correlates with the roughness of the silanated silica surface. These results with silanated silica surfaces were compared with the AFM results for polyethylene and graphite surfaces and on the basis of these experimental efforts, it appears that the nature of these hydrophobic attractive forces is related to surface roughness.     

相结构对十八烷基三氯硅烷分子膜纳米机械强度的影响

目的研究相结构对十八烷基三氯硅烷(OTS)分子膜纳米机械性能的影响。方法分别在冰水混合物温度和室温下制备了OTS分子膜的样品,利用原子力显微镜表征表面形貌,通过施加不同的探针作用力观察相对高度差变化。结果随着针尖作用力的增加,冰水混合物温度下制备的OTS分子膜的相对高度差一直维持在2.02 nm左右;在室温下制备的OTS分子膜,针尖作用力在800 pN以下时,高度值维持在1.73 nm左右;针尖作用力增加到800 pN时,其相对高度差开始下降;当作用力增加到4 nN时,其相对高度差维持在1.44 nm左右。结论有序致密排列的OTS分子岛具有较强的纳米机械强度,无序疏松的OTS分子岛具有较弱的纳米机械强度,易在较大探针作用力下被压变形。     

Advances in piezoelectric thin films for acoustic biosensors,acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.     

表面修饰的ZnPc薄膜晶体管性能研究

以热生长的SiO2作为栅绝缘层,酞菁锌(ZnPc)作为有源层,研究了具有十八烷基三氯硅烷(OTS,C18H37SiCl3)/SiO2双绝缘层结构的有机薄膜晶体管(OTFT)。实验表明,采用OTS可以有效地降低SiO2栅绝缘层的表面能并改善表面的平整度,器件的场效应迁移率提高了3.5倍,漏电流从10-9A降到10-10A,阈值电压降低了5 V,开关电流比从103增加到104。结果显示,具有OTS/SiO2双绝缘层的器件结构能有效改进OTFT的性能。     

Probe‐Based Electro‐Oxidative Lithography of OTS SAMs Deposited onto Transparent ITO Substrates

Transparent conductive oxides like indium tin oxide (ITO) play a pivotal role in a wide range of innovative applications, such as new generations of solar cells. In many of these applications the tailoring of surface properties on the nanometer scale represents a highly desirable target. The local oxidation of self‐assembled monolayers (SAMs) using a scanning probe is a promising technique to achieve surface modifications on the nanometer scale. So far, electro‐oxidative lithography of SAMs has been reported mainly on Si wafers while there are no previous reports on transparent oxides. Here, we report the oxidative lithography of n‐octadecyltrichlorosilane (OTS) SAM deposited onto an ITO layer. A local overoxidation of the substrate is observed while the simultaneously occurring monolayer oxidation is indirectly confirmed by the site‐selective deposition of silver nanoparticles onto electro‐oxidized areas. The process of lithography is compared to that on OTS‐Si substrates and its mechanism is systematically investigated by means of scanning Kelvin probe microscopy (SKPM).     

Superhydrophobic surfaces produced by applying a self-assembled monolayer to silicon micro/nano-textured surfaces

A novel way of producing superhydrophobic surfaces by applying a self-assembled monolayer (SAM) to silicon micro/nano-textured surfaces is presented in this paper. The micro/nano-textured surfaces on silicon substrates were generated by the aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) technique. Octadecyltrichlorosilane (OTS) SAMs were then applied to the textured surfaces by dip coating. The topography and wetting properties of the resulting surfaces were characterized using scanning electron microscopy (SEM) and a video-based contact angle measurement system. The results show that by introducing OTS SAMs on the silicon micro/nano-textured surfaces, superhydrophobic surfaces with water contact angles (WCAs) of 155° were obtained, as compared to the WCAs of OTS-modified smooth silicon surfaces of about 112°. Surface topography was found to directly influence the WCA as predicted by the Cassie-Baxter model.      

表面修饰的ZnPc薄膜晶体管性能研究

以热生长的SiO2作为栅绝缘层,酞菁锌(ZnPc)作为有源层,研究了具有十八烷基三氯硅烷(OTS,C18H37SiCl3)/SiO2双绝缘层结构的有机薄膜晶体管(OTFT)。实验表明,采用OTS可以有效地降低SiO2栅绝缘层的表面能并改善表面的平整度,器件的场效应迁移率提高了3.5倍,漏电流从10-9A降到10-10A,阈值电压降低了5 V,开关电流比从103增加到104。结果显示,具有OTS/SiO2双绝缘层的器件结构能有效改进OTFT的性能。