Large-scale fabrication of highly ordered sub-20 nm noble metal nanoparticles on silica substrates without metallic adhesion layers

Periodic noble metal nanoparticles offer a wide spectrum of applications including chemical and biological sensors,optical devices,and model catalysts due to their extraordinary properties.For sensing purposes and catalytic studies,substrates made of glass or fused-silica are normally required as supports,without the use of metallic adhesion layers.However,precise patterning of such uniform arrays of silica-supported noble metal nanoparticles,especially at sub-100 nm in diameter,is challenging without adhesion layers.In this paper,we report a robust method to large-scale fabricate highly ordered sub-20 nm noble metal nanoparticles,i.e.,gold and platinum,supported on silica substrates without adhesion layers,combining displacement Talbot lithography(DTL)with dry-etching techniques.Periodic photoresist nanocolumns at diameters of~110 nm are patterned on metal-coated oxidized silicon wafers using DTL,and subsequently transferred at a 1:1 ratio into anti-reflection layer coating(BARC)nanocolumns with the formation of nano-sharp tips,using nitrogen plasma etching.These BARC nanocolumns are then used as a mask for etching the deposited metal layer using inclined argon ion-beam etching.We find that increasing the etching time results in coneshaped silica features with metal nanoparticles on the tips at diameters ranging from 100 nm to sub-30 nm,over large areas of 3×3 cm^(2).Moreover,subsequent annealing these sub-30 nm metal nanoparticle arrays at high-temperature results in sub-20 nm metal nanoparticle arrays with~10^(10) uniform particles.

Exploiting biased reptation for continuous flow preparative DNA fractionation in a versatile microfluidic platform

A new approach is presented for preparative,continuous flow fractionation of sub-10-kbp DNA fragments,which exploits the variation in the field-dependent mobility of the DNA molecules based on their length.Orthogonally pulsed electric fields of significantly different magnitudes are applied to a microchip filled with a sieving matrix of 1.2% agarose gel.Using this method,we demonstrate a high-resolution separation of 0.5,1,2,5,and 10 kbp DNA fragments within 2 min.During the separation,DNA fragments are also purified from other ionic species.Preparative fractionation of sub-10-kbp DNA molecules plays an important role in second-generation sequencing.The presented device performs rapid high-resolution fractionation and it can be reliably manufactured with simple microfabrication procedures.

Separation of spermatozoa fromerythrocytes using their tumblingmechanism in a pinch flow fractionationdevice

Men suffering from azoospermia can father a child,by extracting spermatozoa from a testicular biopsy sample.The main complication in this procedure is the presence of an abundance of erythrocytes.Currently,the isolation of the few spermatozoa from the sample is manually performed due to ineffectiveness of filtering methods,making it time consuming and labor intensive.The spermatozoa are smaller in both width and height than any other cell type found in the sample,with a very small difference compared with the erythrocyte for the smallest,making this not the feature to base the extraction on.However,the length of the spermatozoon is 5×larger than the diameter of an erythrocyte and can be utilized.Here we propose a microfluidic chip,in which the tumbling behavior of spermatozoa in pinched flow fractionation is utilized to separate them from the erythrocytes.We show that we can extract 95%of the spermatozoa from a sample containing 2.5%spermatozoa,while removing around 90%of the erythrocytes.By adjusting the flow rates,we are able to increase the collection efficiency while slightly sacrificing the purity,tuning the solution for the available sample in the clinic.