Bioengineered Silicon Diatoms: Adding Photonic Features to a Nanostructured Semiconductive Material for Biomolecular Sensing

Abstract

Native diatoms made of amorphous silica are first converted into silicon structures via magnesiothermic process, preserving the original shape: electron force microscopy analysis performed on silicon-converted diatoms demonstrates their semiconductor behavior. Wet surface chemical treatments are then performed in order to enhance the photoluminescence emission from the resulting silicon diatoms and, at the same time, to allow the immobilization of biological probes, namely proteins and antibodies, via silanization. We demonstrate that light emission from semiconductive silicon diatoms can be used for antibody-antigen recognition, endorsing this material as optoelectronic transducer.

Keywords: Biosensing; Diatoms; Photoluminescence; Silicon.

Fig. 1

a SEM image of a silicon diatom (scale bar 3 μm): the red square underlines the region where AFM and EFM characterizations were performed. b AFM topography (scale bar 2 μm). EFM amplitude at tip bias voltage 0 V (c) and 10 V (d) (scale bar 2 μm): sample morphology appears only at 10 V bias voltage; EFM amplitude distribution at tip bias voltage 0 V (e) and 10 V (f): the Gaussian distribution shows that the average level rises when a voltage of 10 V is applied, indicating the conducting or semiconducting nature of the sample

Fig. 2

Scheme of functionalization procedure used for silicon diatoms

Fig. 3

FTIR spectra of SiD after each functionalization step

Fig. 4

Fluorescence microscopy images of bare (a) and PrA* functionalized (b) SiD. Scale bar 100 μm

Fig. 5

a Comparison between photoluminescence spectra of freshly converted silicon diatoms (SiD), silica diatoms (SiO₂D), and silicon diatoms after incubation in water for 15 days (SiD-OH). b Spectra fitted by a Gaussian multi-peak routine

Fig. 6

a Photoluminescence spectra of silicon diatoms after each functionalization step, from APTES to PrA. b Spectra fitted by a Gaussian multi-peak routine. c Ratio between the intensities of peak 2 and peak 1 for each functionalization step

Fig. 7

a Scheme of fuctionalization of silicon diatoms with anti-His-tag antibody (I) and incubation with His-tagged p53 protein (II). b Photoluminescence spectra of silicon diatoms after antibody-antigen interaction