**Active Accumulation of Spherical Analytes on Plasmonic Hot Spots of Double-Bent Au Strip Arrays by Multiple Dip-Coating**

### **Jinhyung Lee 1,2, Eun-Ah You 1, Do Won Hwang 3, Shinill Kang 2,\* and Jung-Sub Wi 1,\***


Received: 21 March 2019; Accepted: 24 April 2019; Published: 26 April 2019

**Abstract:** To achieve sensitive plasmonic biosensors, it is essential to develop an e fficient method for concentrating analytes in hot spots, as well as to develop plasmonic nanostructures for concentrating light. In this study, target analytes were delivered to the surface of double-bent Au strip arrays by a multiple dip-coating method; they were self-aligned in the valleys between neighboring Au strips by capillary forces. As the valleys not only accommodate target analytes but also host strong electromagnetic fields due to the interaction between adjacent strips, sensitive measurement of target analytes was possible by monitoring changes in the wavelength of a localized surface plasmon resonance. Using the proposed plasmonic sensor and target delivery method, the adsorption and saturation of polystyrene beads 100 nm in size on the sensor surface were monitored by the shift of the resonance wavelength. In addition, the pH-dependent stability of exosomes accumulated on the sensor surface was successfully monitored by changing the pH from 7.4 to 4.0.

**Keywords:** localized surface plasmon resonance; dip-coating; capillary force; exosome
