Seedless gold nanostars with seed-like advantages for biosensing applications

Abstract

Gold nanostars (AuNSs) are seen as promising building blocks for biosensors with potential for easy readouts based on naked-eye and ultraviolet-visible spectroscopy detection. We present a seedless synthesis strategy for AuNSs that has the advantages of the seeded methods. The method used ascorbic acid as a reducing agent and silver nitrate as an anisotropic growth control assisting agent. AuNSs with multiple branches and a diameter of 59 nm were produced. They showed good stability when capped with PVP and modified with an enzyme in relatively strong ionic conditions. We investigated their application in plasmonic sensing by modifying them with glucose oxidase and detection of glucose. The AuNSs were found to be a good scaffold for the enzyme, proved to be stable and sensitive as transducers. Thus, the AuNSs showed good promise for further applications in plasmonic biosensing for in vivo biomedical diagnosis.

Keywords: biosensors; glucose oxidase; gold nanostars; plasmonic; synthesis.

Figure 1.

Comparison of UV–vis spectra of seeded-AuNSs (a), seedless-AuNSs (b) and HEPES-AuNSs (c).

Figure 2.

TEM images of seeded-AuNSs (a), seedless-AuNSs (b) and HEPES-AuNSs (c). The insets show the magnified TEM images of the respective AuNSs at 10 nm.

Figure 3.

(a) Normalized UV–vis spectra of the control seedless-AuNSs and GOx-modified seedless-AuNSs. (b) Agarose gel electrophoresis of the control nanostars and those modified with GOx. (c) The hydrodynamic diameters of the nanostars before and after modification with GOx.

Figure 4.

Images showing the stability of the stars in salt (a) for control seedless-AuNSs and (b) for GOx-modified seedless-AuNSs.

Figure 5.

Feasibility of glucose sensing with GOx-modified nanosensors. Glucose: 2.5 mM, Ag⁺: 0.1 mM and pH: >9.

Scheme 1.

Schematic of plasmonic colorimetric strategy for enzyme-guided growth of Ag⁰ on AuNS and LSPR blue-shift.

Figure 6.

(a) Normalized UV–vis spectra of GOx-modified seedless-AuNSs showing blue-shift on reacting with different concentrations of glucose. (b) Plot of glucose concentration versus inverse maximum absorption. (c) TEM images of the seedless-AuNSs in the presence of increasing glucose concentrations: (I) 0 mM, (II) 1.25 mM, (III) 5 mM and (IV) 8.75 mM. (d) EDS analysis of C-I and III of the seedless-AuNSs.