Construction Of Micro/Nanostructures On The Inner Wall Of Microchannels And Their Functional Design

As one of the most advanced areas of science and technology, microfluidic technology have found many applications in various fields, ranging from life sciences to industrial chemical synthesis due to their unique advantages such as high-throughput and low-consumption. Microchannel, as an important component of microfluidic device, was just pure inner surface supplied as microspace at the early stage. However, with the development of microfluidic technology and the increasing demands for complex and improved structural functionalities of microfluidic systems for specific biological applications, modification of the inner wall of microchannels (IWMs) is necessary. Geometry modification of the microchannel is constructing specific fine micro/nano structures on the IWM. Compared with simply coating a layer of functional film on the IWMs, fabrication of micro/nanostructures perpendicular to the IWM and further grating functional groups or molecules on them can not only make the microchannel possess more functionalities, but also be considered as an important research direction promoting the microfluidic technology advancement. Various micro/nanofabrication techniques such as etching, lithography and soft lithography have been used for manufacturing micro/nanostructures to physically modify microchannel. But most of these methods are not flexible enough and are difficult to apply to a closed system such as a long microcapillary with small inlet and outlet. Moreover, the sealing process of the opened microchannel will be bound to cause damage to the formed micro/nanostructure. In this paper, a wet chemical route was used to fabricate specific micro/nanostructures on the IWM. Certain surface modifications were carried out to functionalize the constructed micro/nanostructures, and thus microchannel-based photocatalysis microreactor and micro protein enrichment device were successfully designed. Incorporating one-dimensional (1D) nanomaterials into the closed microchannel and utilizing the latest research achievements of micro/nanodevices comprising of 1D nanomaterials will open up a new way to modify and functionalize the microchannels.ZnO nanorod arrays and distribution-tunable ZnO nanorod flowers were fabricated on the IWMs through a wet chemical route. A layer of ZnO seed film well covered on the IWM was prepared using the ethanol solutions of NaOH and Zn(AC)2·2H2O as the reactants; clusters of ZnO crystal seeds with different densities on the IWM were formed via the reverse microemulison method in which the dispersity of the micelles, the high temperature demulsification technique and the particle agglomeration all contributed to the formation. The dispersing density of crystal seeds on a substrate is of crucial importance to the selective growth and ultimate shape and morphology of crystal. So, on the IWM well covered with ZnO seed film, perpendicular growth of ZnO nanorod arrays were obtained, while on the IWM with well dispersed ZnO seed clusters, distribution density controllable ZnO nanorod flowers were fabricated. It was found that the molar ratio of water to surfactant denoted as w is an important factor which determines the dispersion of ZnO seeds and the distribution of ZnO nanorod flowers. By changing the value of w, the size of the water droplets was changed and so was the size of the particles. Also because of the different adhesion forces of the microchannel to particles with different sizes, the density of the clusters of crystal seeds was well tailored, and thus the distribution density of the final ZnO nanorod arrays was controlled. As the value of w increased, the density of the crystal seeds became bigger and the distribution of the nanorods denser. The results provide a simple, original and versatile route to generate a nano-patterned substrate in quasi closed microspace.On the base of ZnO nanorod arrays, Pt/ZnO, TiO2/ZnO and ZnO@ZnS nanorod arrays were also fabricated on the IWM. These nanorod arrays modified microchannels were used as photocatalysis microreactors. Methylene blue (MB) and 4-chlorobenzene were chosen as model compounds to evaluate the photocatalytic activity of the microreactors.(a) The microreactor based on ZnO nanorod arrays modified microchannel was used to photocatalyze 5 ppm MB solution. The results show that at the residence time (RT) of 100 s, the photodegradation rate of MB was over 100%and when it was repeatedly used for 180 h, the photocatalytic efficiency was still more than 80%.(b) The microreactor based on distribution-tunable ZnO nanorod flowers modified microchannel was used to photocatalyze 5 ppm MB solution. When RT increased to more than 110 s, the photodegradation rates of MB were close to 100%for all three microreactors. However, when RT was between 25 and 110 s, microreactor M (with medium-density ZnO) showed higher photocatalytic performance than microreactor H (with high-density ZnO) and microreactor L (with medium-density ZnO), which means that the distribution density of ZnO nanorod flowers could indeed affect the performance of the as-designed microfluidic device.(c) The microreactor based on Pt/ZnO nanorod arrays modified microchannel was used to photocatalyze 5 ppm MB solution. With RT of 35 s, the MB solution could be completely decomposed. The Pt noble metal here acts as a sink for photoinduced charge carriers, promoting interfacial charge-transfer processes.(d) The microreactor based on TiO2/ZnO nanorod arrays modified microchannel was used to photocatalyze 5 ppm MB solution. Compared with pure ZnO nanorod arrays, the relatively more superior photocatalytic activity of the ZnO/TiO2 nanorod-modified microreactor was attributed to the combination of two semiconductors decreasing the recombination rate of photoinduced electrons and holes. Microreactor based on TiO2/ZnO-3 (TiO2 sol coating three times) showed the highest photocatalytic activity among all the microreactors based on TiO2/ZnO nanorod arrays with different TiO2 sol coating circles. For the microreactor based on TiO2/ZnO-3, RT= 20 s was sufficient to completely photodegrade MB molecules and when it was repeatedly used for 100 h, the photocatalytic efficiency of the microreactor was still more than 90%.(e) The microreactor based on ZnO@ZnS core-shell nanorod arrays modified microchannel was used to photocatalyze 10 ppm MB solution and 10 ppm 4-chlorophenol solution. With RT of 120 s, the photodegradation rates of MB and 4-chlorophenol were 100%and 78%, respectively.It is obvious that the microreactor based on TiO2/ZnO nanorod arrays displayed the highest photocatalytic activity among all the microreactors based on different nanorod arrays modified microchannels. Meanwhile, all the nanorod arrays showed strong washing resistance and desirable stability during the continuously recycling in photocatalysis.A continuous-flow method was used to prepare TiO2/ZnO nanorod arrays on IWMs with different coating thicknesses. This was achieved by controlling the flow duration of a TiO2 sol in a microchannel containing preformed ZnO nanorod arrays as the supports for the immobilization of TiO2. A novel lab-on-a-chip device based on the microchannel modified with ZnO/TiO2 was designed to selectively bind and capture phosphorpeptides (PPs) from tryptic digests. This protocol allowed uninterrupted PP introduction, capture and enrichment by an automatic and continuous-flow operating mode through the microchannel. It showed great selectivity, sensitivity and durability for the enrichment of PPs from tryptic protein digests. Amounts of PPs sufficient for MALDI-MS analysis could be enriched with a RT of just 30 s. A RT of 60 s was determined to be appropriate for eluting the conjugated PPs from the CM. In view of its high durability and continuous-flow operation, this lab-on-a-chip device may achieve cost-effective, high-throughput PP enrichment from large volumes of complex clinical samples. It will also work as a convenient platform for the rapid and specific capture of PPs prior to MS analysis.Highly-ordered ZnO@ZnS core-shell nanorod arrays were fabricated on the IWMs through an in situ conversion method with preformed ZnO nanorod arrays as the template and thioacetamide as the sulfur source. When the ZnO@ZnS nanord arrays exposed to sodium thioglycollate (ST) solution, ST-ZnO@ZnS nanorod arrays were generated on the IWC. By driving the fresh prepared Ag colloidal to the microchannel with ST-capped ZnO@ZnS nanorod arrays, Ag-loaded ST-capped ZnO@ZnS nanorod arrays on the IWC were simply obtained. The microfluidic device based on the nanorod arrays modified capillary microchannel was utilized as a novel biomolecule trapping device. Bovine serum albumin (BSA) was chosen as a model albumin to test the capture ability of the device to target protein. The microfluidic device based on ST-ZnO@ZnS nanorod arrays displayed high capture ability to BSA and high performance durability in the continuous trapping of BSA. The microfluidic device based on Ag-ST-ZnO@ZnS nanorod arrays on the IWC was also successfully applied to concentrate trace amount of BSA and the vibrational bands in the SERS results confirmed the trapped BSA. The device based on core-shell nanorod arrays on the IWC not only realized the continuous high-throughput separation of proteins from large volume complex biological matrices, but also put forward a new route to concentrate and detect trace amount of protein.