Silk fibroin-based optical anti-counterfeiting mark and preparation method thereof

Abstract

The invention provides a silk fibroin-based anti-counterfeiting mark comprising a silk fibroin film layer and a gold film layer located on the silk fibroin film layer, and the area of the gold film layer is less than that of the silk fibroin film layer. The inventive also provides a method for preparing the silk fibroin-based optical anti-counterfeiting mark, the method comprises preparing an aqueous silk fibroin solution, coating the aqueous silk fibroin solution onto a substrate to obtain a silk fibroin film, and sputtering a layer of gold film on the silk fibroin film with a mask to obtain the silk fibroin-based optical anti-counterfeiting mark. In the invention a thin layer of Au film is sputtered on a silk fibroin film such that an anti-counterfeiting mark pattern appears at a high humidity, the method is simple and can significantly the production cost of optical anti-counterfeiting mark.

Claims

1. A method of preparing a silk fibroin-based optical anti-counterfeiting mark comprising steps of: (1) preparing an aqueous silk fibroin solution; (2) coating the aqueous silk fibroin solution onto a substrate to obtain a silk fibroin film; and (3) sputtering a layer of gold film on the silk fibroin film obtained in step (2) with a mask to obtain the silk fibroin-based optical anti-counterfeiting mark, wherein the silk fibroin film layer has a thickness of 100-500 nm; the gold film layer has a thickness of 1-5 nm; and a humidity at which a pattern of the silk fibroin-based optical anti-counterfeiting mark is revealed is 65%-85%, and wherein in the step (2), the substrate is a silicon wafer.

2. The method as claimed in claim 1, wherein in the step (1), a mass concentration of the aqueous silk fibroin solution is 4-20%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view showing the process of preparing an anti-counterfeiting mark according to the present invention;

(2) FIG. 2 shows an optical photograph of a silk fibroin film at a low and high humidity according to the invention, wherein a layer of triangular Au pattern is sputtered on the silk fibroin film; and

(3) FIG. 3 shows an optical photograph of a fibroin film at a low and high humidity according to the invention, wherein a layer of complicated Au pattern is sputtered on the silk fibroin film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The invention will be further illustrated in more detail with reference to accompanying drawings. It is noted that, the following embodiments only are intended for purposes of illustration and are not intended to limit the scope of the invention.

(5) In the embodiments of the invention, the silk fibroin aqueous solution was prepared as follows:

(6) silkworm cocoons were cut into pieces of about 1 cm.sup.2 and added into a boiled NaHCO.sub.3 solution of 0.5 wt %. After boiling for 45 mins, the degummed silk was washed with deionized water 4 to 5 times. A picric acid-carmine solution was used for detection until the silk was completely degummed. After the degumming was completed, the silk fibroin was placed in an oven at 40 C. for drying. An amount of the degummed silk was weighed and fully immersed in a container containing a 10 M LiBr solution at a liquor ratio of 1:10, then the container was maintained at a constant temperature of 60 C. for one hour. Subsequently, the solution was dialyzed in a dialysis bag with a molecular weight cut-off of 7000 for 3 days, and then centrifuged at 9000 r/min for 20 min to obtain the aqueous silk fibroin solution, finally the obtained aqueous silk fibroin solution was placed in a refrigerator at 4 C. for storage.

Embodiment 1

(7) 1 ml of silk fibroin solution with a concentration of 7.5 wt % was spin-coated on a silicon wafer of 2 cm by 2 cm using a spin coater at a spin-coating rate of 3000 rpm, and then naturally dried at 25 C. to obtain a silk fibroin film with the orange color. An Au film layer with a thickness of about 2 nm was then sputtered on the surface of the silk fibroin film using a mask with a shape of triangle by an ion sputter equipment E-1045 to obtain a silk fibroin-based optical anti-counterfeiting mark, the sputtering current was 10 mA, the sputtering time was 10 s, and the sputtering speed was 10 nm/min. Finally, a triangular pattern was clearly revealed at a humidity above 65%.

(8) FIG. 2 is an optical photograph of the silk fibroin film having an triangular Au film obtained in the embodiment 1 of the present invention at a humidity of 20% and 90%. The size is 2 cm by 2 cm, and it can be seen from the FIG. 1 that during the increase of humidity from 20% to 90%, the color in the pattern-free area changes from orange to light blue, and the color in the area with a triangular pattern changes from orange to blue.

Embodiment 2

(9) 1 ml of silk fibroin solution with a concentration of 10 wt % was spin-coated on a silicon wafer of 2 cm by 2 cm using a spin coater at a spin-coating rate of 3500 rpm, and then naturally dried at 25 C. to obtain a silk fibroin film with the yellow color. An Au film layer with a thickness of 2.5 nm was then sputtered on the surface of the fibroin film using a mask with a complicated logo shape by an ion sputter equipment E-1045 to obtain a silk fibroin-based optical anti-counterfeiting mark, the sputtering current was 10 mA, the sputtering time was 15 s, and the sputtering speed was 10 nm/min. Finally, a logo pattern was clearly revealed at a humidity of 85%.

(10) FIG. 3 is an optical photograph of the fibroin film having an Au film with a complicated logo shape obtained in the embodiment 2 of the invention at a humidity of 30% and 85%. The size is 2 cm by 2 cm, and it can be seen from the FIG. 3 that during the increase of humidity from 30% to 85%, the color in the pattern-free area changes from yellow to blue and the color in the area with a logo pattern substantially remains yellow.

Embodiment 3

(11) 1 ml of fibroin solution with a concentration of 20 wt % was spin-coated on a silicon wafer of 2 cm by 2 cm using a spin coater at a spin-coating rate of 4000 rpm, and then naturally dried at 25 C. to obtain a silk fibroin film with the purple color. An Au film layer with a thickness of 5 nm was then sputtered on the surface of the silk fibroin film using a mask with a shape of square by an ion sputter equipment E-1045 to obtain a silk fibroin-based optical anti-counterfeiting mark, the sputtering current was 10 mA, the sputtering time was 30 s, and the sputtering speed was 10 nm/min. Finally, a square pattern was clearly revealed at a humidity above 65%.

(12) The above preferred embodiments are described for illustration only, and are not intended to limit the scope of the invention. It should be understood, for a person skilled in the art, that various improvements or variations can be made therein without departing from the spirit and scope of the invention, and these improvements or variations should be covered within the protecting scope of the invention.