New conductive filament ready-to-use for 3D-printing electrochemical (bio)sensors: Towards the detection of SARS-CoV-2

Abstract

The 3D printing technology has gained ground due to its wide range of applicability. The development of new conductive filaments contributes significantly to the production of improved electrochemical devices. In this context, we report a simple method to producing an efficient conductive filament, containing graphite within the polymer matrix of PLA, and applied in conjunction with 3D printing technology to generate (bio)sensors without the need for surface activation. The proposed method for producing the conductive filament consists of four steps: (i) mixing graphite and PLA in a heated reflux system; (ii) recrystallization of the composite; (iii) drying and; (iv) extrusion. The produced filament was used for the manufacture of electrochemical 3D printed sensors. The filament and sensor were characterized by physicochemical techniques, such as SEM, TGA, Raman, FTIR as well as electrochemical techniques (EIS and CV). Finally, as a proof-of-concept, the fabricated 3D-printed sensor was applied for the determination of uric acid and dopamine in synthetic urine and used as a platform for the development of a biosensor for the detection of SARS-CoV-2. The developed sensors, without pre-treatment, provided linear ranges of 0.5-150.0 and 5.0-50.0 μmol L^-1, with low LOD values (0.07 and 0.11 μmol L^-1), for uric acid and dopamine, respectively. The developed biosensor successfully detected SARS-CoV-2 S protein, with a linear range from 5.0 to 75.0 nmol L^-1 (0.38 μg mL^-1 to 5.74 μg mL^-1) and LOD of 1.36 nmol L^-1 (0.10 μg mL^-1) and sensitivity of 0.17 μA nmol^-1 L (0.01 μA μg^-1 mL). Therefore, the lab-made produced and the ready-to-use conductive filament is promising and can become an alternative route for the production of different 3D electrochemical (bio)sensors and other types of conductive devices by 3D printing.

Keywords: 3D printing; COVID-19 diagnosis; Graphite; Lab-made conductive filament; PLA.

Graphical abstract

Fig. 1

Representative scheme for the production of the improved Gpt-PLA conductive filaments. (A) incorporation of graphite powder on PLA and a reflux system under constant stirring and heating; (B) recrystallization of the composite (Gpt-PLA) in ethanol; (C) filtration of the composite constantly washing with ethanol; (D) drying step on the oven at 50 °C; (E) cut into small parts; (F) composite extrusion step and (G) 3D printing of the electrochemical sensor.

Fig. 2

Representative scheme of the involved steps in the fabrication of the immunosensor.

Fig. 3

Physicochemical characterizations: A) Thermogravimetric analyses for raw PLA, graphite powder, and GP-PLA filaments containing 1, 15, 25, 30, 35, 40, 50, 55, 60 %wt. graphite; B) Raman spectra for Gpt-PLA (40% wt.) filament (red line) and 3D printed electrode (black line); C) FTIR spectra for raw PLA, graphite powder, Gpt-PLA (40% wt.) filament and 3D printed electrode; D) and E) SEM images of 40% wt. Gpt-PLA 3D printed electrode after 2000 (D) and 8000 (E) amplification factors, and F) Contact angle image. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

Cyclic voltammograms for 1.0 mmol L⁻¹ [Fe(CN)₆]^3−/4− in 0.1 mol L⁻¹ KCl in A) Gpt-PLA, CB-PLA, and G-PLA after polishing in sandpaper; B) Gpt-PLA, CB-PLA, and G-PLA after electrochemical pre-treatment and; C) Gpt-PLA before and after electrochemical treatment. Scan rate: 50 mV s⁻¹.

Fig. 5

Cyclic voltammograms for 1.0 mmol L⁻¹ UA in 0.1 mol L⁻¹ BR buffer (pH 2.0) on 3D printed Gpt-PLA and G-PLA and CB-PLA before and after electrochemical pre-treatment. Scan rate: 50 mV s⁻¹.

Fig. 6

Differential pulse voltammograms for increasing concentrations of UA (0.5, 1.0, 5.0, 10.0, 20.0, 30.0, 40.0, 50.0, 75.0, 100.0, 125.0 and 150.0 μmol L⁻¹) in 0.1 mol L⁻¹ BR buffer (pH 2.0). DPV parameters: 80 mV (modulation amplitude); 30 ms (modulation time); 5 mV (step potential).

Fig. 7

Cyclic voltammetric recordings in presence of 1.0 mmol L⁻¹ FcMeOH in 0.1 mol L⁻¹ KCl after each immobilization step. Scan rate: 100 mV s⁻¹.

Fig. 8

Cyclic voltammograms recorded in presence of 1.0 mmol L⁻¹ FcMeOH in 0.1 mol L⁻¹ KCl using the fabricated immunosensor for increasing concentrations of antigen (5.0, 10.0, 30.0, 50.0 and 75.0 nmol L⁻¹); Scan rate: 100 mV s⁻¹.