Controllable Fabrication Of Aluminum Nanoparticle Array And Its Application In Surface Plasmon-Enhanced Fluorescence

Aluminum(Al)is the most abundant metallic element in nature,which is widely used in daily life because of its low price and excellent physical properties.At the same time,Al nanoparticles also exhibit strong local surface plasmon resonance(LSPR)properties.Due to high free electron density and unique interband transition of A1,LSPR properties of Al nanoparticles can be tuned in a wide spectral ranging from deep ultraviolet(～150 nm)to near infrared,which fills the blank of the application of gold and silver nanoparticles in deep UV surface plasmons.Al nanoparticles have showed excellent performance in the fields of surface-enhanced Raman spectroscopy,photocatalysis,solar cells,light-emitting devices and so on.Especially in the application of local surface plasmon-enhanced fluorescence,the self-passivated nanoscale oxide layer of Al nanoparticles can interact with a variety of functional groups to fix signal molecules and effectively prevent fluorescence quenching.Thus,it avoids complex chemical modification or physical coating of gold or silver nanostructures in fluorescence enhancement applications.By changing the size,morphology and dielectric environment of Al nanoparticles,the wavelength of LSPR peak can be finely adjusted.There are two main methods for Al nanoparticles:(1)"Top-down" etching techniques(such as electron beam lithography),this kind of technology can fabricate simple-shaped Al nanoparticles for scientific research,which have a high cost limiting the large-scale application of Al nanoparticles;(2)Wet chemical synthesis,because the nucleation and growth rate of Al nanocrystals are difficult to control,and there is a lack of effective surface ligand to achieve the selective growth of crystal facet.This kind of technology cannot synthesize Al nanoparticles with uniform size and morphology.Therefore,there is an urgent need for a simple and reliable method for large-scale preparation of Al nanoparticles with controllable size and adjustable morphologies,which can promote the further research and wide application of LSPR properties of Al nanoparticles.In this paper,based on the electrostatic self-assembly technology of colloidal particles on the substrate surface,we developed a simple and reliable method to achieve the fabrication of large-area Al nanoparticle arrays with different sizes and morphologies.The Al nanoparticle arrays fabricated by this method have excellent LSPR properties and fluorescence enhancement effect,showing great potential in the application of surface plasmon-enhanced fluorescence.The research contents are as follows:(1)We developed a colloidal particles self-assembly template method to fabricate Al nanoparticle arrays.Colloidal particles with different sizes and morphologies were driven by electrostatic force to form uniform monodispersed self-assembly nanoparticle arrays on the substrate.Then,through common and simple processes such as spin-coating,plasma etching,and thermal evaporation,the self-assembly nanoparticle arrays were used as sacrificial template to fabricate large-area uniform monodisperse Al nanoparticle arrays with controllable size(36 um～222 nm)and adjustable morphology(nanobowl,nanocuboid,nanodisk)of which the LSPR peaks(wide spectral range from UV to visible)were finely adjusted.In conclude,this method overcomes the disadvantage that "topdown" etching technique cannot fabricate large-area nanoparticle arrays with complex morphologies,and relieved the dilemma that the size and morphology of Al nanoparticles cannot be controlled by wet chemical synthesis technique.(2)The 131 nm Al nanobowl array with a wide LSPR was fabricated by the colloid particle self-assembly template method.The abundant "hot spots" of Al nanobowl array have strong local electromagnetic field enhancement.By matching the LSPR peak of Al nanobowl array with the excitation and emission peaks of fluorescent molecules,Al nanobowl array achieved 1932 times fluorescence enhancement compared with silica substrate and highly sensitive detection of 5-carboxyfluorescein which emits green light as low as 78 pM.Al nanobowl array also achieved 199 times fluorescence enhancement compared with silica substrate and highly sensitive detection of acid fuchsin which emits red light as low as 0.31 nM.By increasing the interparticle distance between the Al nanobowls on the substrate surface,we achieved imaging of the scattering signal of single Al nanobowl and the fluorescence signal of the fluorescent molecules on the surface of single Al nanobowl,and collected clear scattering and fluorescence spectra of single Al nanobowl.In conclusion,we prove that Al nanoparticles have great fluorescence enhancement effect and highly sensitive detection for fluorescent molecules excited and emitting in visible light region,which demonstrate the great potential of Al nanoparticles in biosensing,single particle sensing and other applications.