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Superstructural Raman Nanosensors with Integrated Dual Functions for Ultrasensitive Detection and Tunable Release of Molecules Jing Liu, Jianhe Guo, Guowen Meng, and Donglei Fan Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b01979 • Publication Date (Web): 29 Jun 2018 Downloaded from http://pubs.acs.org on July 1, 2018
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Chemistry of Materials
Superstructural Raman Nanosensors with Integrated Dual Functions for Ultrasensitive Detection and Tunable Release of Molecules Jing Liu†, ‡, ∥, Jianhe Guo†, ∥, Guowen Meng ‡, § and Donglei Fan*, †, ⊥ ∥
These authors contributed equally to this work
AUTHOR ADDRESS: †
Materials Science and Engineering Program, the University of Texas at Austin, Austin, TX 78712, USA
‡
Key Laboratory of Materials Physics, and Anhui Key Laboratory of Nanomaterials and Nanotechnology, Institute of Solid State Physics, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Hefei, 230031, China § ⊥
University of Science and Technology of China, Hefei, 230026, China Department of Mechanical Engineering, the University of Texas at Austin, Austin, TX 78712, USA
ABSTRACT: It is highly desirable, while extremely difficult to actively control the release dynamics of molecules from nanoparticle-carriers and to monitor the release process in real time. In this work, we report the design, fabrication, and manipulation of a superstructural Raman nanosensor, offering integrated dual functions in ultra-sensitive biodetection and dynamic control in molecule release. The device has a designed porous superstructure, consisting of gold (Au) nanorod cores and silica shells embedded with arrays of nanocavities arranged in concentric layers in three-dimensions (3D), where high-density plasmonic silver (Ag) nanoparticles are grown both in the nanocavities and on the outer surfaces. The Ag nanoparticles provide substantially enhanced Raman sensitivity for detection of molecules, owing to the large number of hotspots, as well as the near-field coupling of Ag nanoparticles due to their 3D concentric arrangement. Furthermore, by controlling the external electric field, the release of molecules can be facilely controlled at tunable rates owing to the induced electrokinetics at the junctions of Ag nanoparticles. Finally, the biosensing-release-unibody devices can be readily motorized, including transport and rotation, which opens new opportunities for single-cell bioresearch and precision medicine.
symmetric nanostars.21-22 Well reproducible Raman nanosensors with enhancement factor as high as 109-1011 have been reported.23-24 Nevertheless, current research efforts largely focus on improving sensing performance of Raman nanosensors in terms of enhancement factors and reproducibility. To fully realize the potential of SERS techniques, it has triggered substantial interest to investigate new device paradigm of Raman sensing devices that provide multiple integrated functions.25-29 Particularly, a dual functional device scheme that offers Raman sensing capability integrated with active manipulation of molecules is challenging, while of great potential for many applications.30-31 Controlled release of biomolecules from nanoparticles have received substantial attention from interdisciplinary
INTRODUCTION Surface enhanced Raman scattering/spectroscopy (SERS) is one of the most promising sensing techniques that can reveal both chemistry and quantity of multiplex molecules in a noninvasive, sensitive, and label-free manner.1-6 The coherent oscillation of electrons in the conduction band of metallic nanoparticles boosts the electromagnetic fields (E) in the vicinity of nanoparticles and their narrow junctions. The locations with ultrahigh electromagnetic field are the socalled plasmonic hotspots. When molecules reside at the hotspots, their Raman spectra are greatly enhanced, with an approximately E4 dependence.7-9 It has been of great interest to design and fabricate high-performance SERS substrates. To date, a variety of noble metallic substrates have been fabricated for SERS detection, including nanoparticles,10-14 nanorods,15-18 core-shell nanostructures,19-20 and highly
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SCHEME 1. Flow chart of the fabrication process of the nanoporous superstructural Raman sensors research communities of chemistry, materials, biology and engineering.32-34 The great interest in utilizing nanoparticles as molecule carriers arises due to their molecular and cellular relevant size, which allows precision loading of biochemicals and subsequent release at targeted locations, such as to a single live cell amidst many.35-38 It is even more potent to actively control the release of biomolecules from nanoparticles. Innovative approaches have been reported to trigger the release of biochemicals from nanoparticles by designed surface functionalization and unique responses of nanoparticles to their environment.32-34 For instance, the controllable release of molecule by near-infrared light based on the photothermal effect of gold nanocages was reported recently.39 A similar approach was also used for intracellular release of oligonucleotides.40-43 The release of molecule can also be triggered by magnetic fields, which induce mechanical deformation of magnetic hydrogel composites or generate heat due to Néel and Brownian relaxation.44-45 Controlling electric potential is another method to control the molecule release dynamically based on the electrochemical reduction-oxidation process on electrode surface.46 Ultrasound waves have also been reported to trigger the release of molecules through mechanical effects generated by cavitation phenomena or radiation forces.47-48 Nevertheless, it remains a grand challenge to control the release dynamics of biomolecules in a tunable fashion and monitor the release process in-situ and in real time with ultrasensitivity. In this work, we report a Raman sensing device that not only detects molecules with ultrasensitivity and high reproducibility, but also provides enhanced capacitance to carry biomolecules and actively control their release dynamics. The device is made of a nanoporous superstructural composite, consisting of an Au nanorod core, a nanoporous superstructural silica shell, and large arrays of
plasmonic Ag nanoparticles as shown in Scheme 1(a-f). The nanoporous silica superstructure with vast embedded nanocavities is created strategically by alternately coating silica and assembling nanospheres on the Au nanorod cores. After calcination, the polystyrene (PS) nanospheres are removed. This process generates high-density nanocavities in silica, arranged concentrically in 3D around the Au nanorod. The nanocavities provide enhanced 3D nanospaces for sustaining biomolecules, as well as large surface areas for the growth of the plasmonic Ag nanoparticles. A three-fold enhancement of molecule loading is achieved compared to that of a solid control sample. The large number of Ag nanoparticles grown on both the inner nanocavities and outer surface of the silica shell [Scheme 1(f-g)], offers substantially enhanced Raman sensitivity, owing to the increased number of hotspots and their near-field electromagnetic coupling. In an external AC electric field, the Ag nanoparticles also actively manipulate molecules and tune the release rate due to the induced electrokinetic effect. Finally, the dual functional superstructural Raman nanosensors are manipulated, i.e. transport to a specific location and rotate at a controlled speed, desirable for location-predicable sensing and biomolecule delivery for many potential applications in precision medicine,38, 49 mechano-biology,50-51 cell-cell communications,52 and system biology.53-54 RESULTS AND DISCUSSION Design, Fabrication, and Characterization The design of each component in the porous superstructural Raman nanosensor serves for a purpose. The long metallic core can be readily polarized and manipulated in external electric fields. The nanoporous silica shell supports the growth of large number of plasmonic Ag
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Chemistry of Materials
95/µm2. Then, by repeating the process of silica coating and nanosphere assembling, multiple layers of nanospheres can be rationally embedded in the silica forming into a 3D superstructure. As shown in Figure 1(c), the second layer of PS nanospheres with a density of ~ 103/µm2 is successfully assembled on the outer surface of the silica shell, which has the first impregnated layer of nanospheres in Figure 1(b). To fully cover the PS nanospheres assembled on the Au/silica core-shells, the thickness of the silica nanoshells is increased to 40-50 nm. After coating the outmost layer of silica, the PS nanospheres are removed at 550 ˚C in air, forming nanoporous superstructures with mono-dispersed nanocavities [Figure 1(d)]. The final diameter of the porous silica superstructures is around 850 nm. The corrugated surface due to the embedment of nanocavities could enhance the loading of plasmonic Ag nanoparticles [Figure 1(d)]. Finally, the Ag nanoparticles are grown both in the inner nanocavities and on the outer surfaces of the porous silica superstructures [Figure 1(e-g)]. They are densely distributed with an average diameter of ~27 nm and junctions ranging from 0.5 nm to 5 nm on the surface of the porous silica superstructures. We know that electromagnetic fields increase dramatically with the narrowing of the junctions of Ag nanoparticles. If we only consider the nanojunctions of
