All-printed multiplexed electrocatalytic biosensors with rationally designed nanoparticle inks.

Inkjet printing, capable of rapid and template-free fabrication with high resolution and low material waste, is a promising method to construct electrochemical biosensor devices. However, the construction of fully inkjet-printed electrochemical biosensor remains a challenge owing to the lack of appropriate inks, especially the sensing inks of bioactive materials. Herein, we demonstrate a fully inkjet-printed, integrated and multiplexed electrochemical biosensor by combining rationally designed nanoparticle Inks. The stable gold (Au) nanoparticles ink with lower sintering temperature is prepared by using L-cysteine as stabilizer, and it is used to print the interconnects, the counter electrodes, and the working electrodes. The SU-8 ink is used to serve as dielectric layer for the biosensor, whereas the silver electrode is printed on the Au electrode by using commercially silver nanoparticles ink before it is chlorinated to prepare Ag/AgCl reference electrode. Moreover, we synthesize an inkjet-printable and electroactive ink, by the 'one-pot method', which is composed of conductive poly 6-aminoindole (PIn-6-NH2) and gold-palladium (Au-Pd) alloy nanoparticle (Au-Pd@PIn-6-NH2) to enhance the sensing performance of gold electrode towards hydrogen peroxide (H2O2). Especially, the amino groups in PIn-6-NH2can be further used to immobilizing glucose oxidase (GOx) and lactic acid oxidase (LOx) by glutaraldehyde to prepare printable sensing ink for the detection of glucose and lactate. The fully inkjet-printed electrochemical biosensor enabled by advanced inks can simultaneously detect glucose and lactate with good sensitivity and selectivity, as well as facile and scalable fabrication, showing great promise for metabolic monitoring.

Template-free, controllable and scalable synthesis of poly(5-aminoindole) nanoparticles for printable electrochemical immunosensor with ultra-high sensitivity.

Conductive polymer polyindole derivatives have good conductivities and abundant functional groups, which would offer great potential for versatile applications including biosensors, bioelectronics and energy devices. However, the polyindole derivatives are mainly synthesized by the electropolymerization method on conductive electrode surfaces, which limits large-scale synthesis and practical applications. Herein, we explore a strategy of template-free, controllable and scalable synthesis of poly-5-aminoindole (PIn-5-NH2) nanoparticles (NPs) and demonstrate the application of PIn-5-NH2 NPs in printable multiplexed electrochemical biosensors with ultra-high sensitivity. The synthesis of PIn-5-NH2 NPs is based on a self-templated method since the In-5-NH2 monomer with amphiphilic structures can form micelles by self-assembly in an aqueous solution. The diameter of PIn-5-NH2 NPs could be controlled by adjusting the synthesis conditions, such as monomer concentration, oxidant/monomer ratio and reaction time. The PIn-5-NH2 NPs possess distinct features, including good conductivity, large surface area, and abundant -NH2 functional groups for covalent binding of the antibody, and therefore offer substantial possibilities for developing an all-printable process to fabricate multiplexed electrochemical immunosensors. The printed multiplexed electrochemical immunosensors on the basis of the aqueous suspension of PIn-5-NH2 NPs linked with antibodies can simultaneously detect multiple cancer markers, and exhibit high sensitivity and good selectivity. Our facile and scalable synthesis strategy would offer great opportunities for versatile applications of PIn-5-NH2 NPs.

A highly sensitive label-free electrochemical immunosensor based on poly(indole-5-carboxylicacid) with ultra-high redox stability.

The high stability of redox signal is one of the most crucial factors in construction of electrochemical immunosensors. However, the redox-active species usually show low stability and poor conductivity, which inhibits their application in electrochemical immunosensors. In this work, we report that the conductive polymer poly(indole-5-carboxylic acid) (PIn-5-COOH) possesses ultra-high redox stability. The redox signal of PIn-5-COOH could remain 96.03% after 500 cyclic voltammery (CV) cycles in buffer solution with pH of 6.2, while the redox signals in most of the previous reports only remained less than 90% after 50 CV cycles. Our mechanism investigation indicated that the ultra-high redox stability of PIn-5-COOH should be attributed to its stable structure. The electrochemical immunosensors fabricated with PIn-5-COOH/MWCNTs-COOH nanocomposite showed a wide linear range from 0.001 ng mL-1 to 100 ng mL-1 and a low detection limit of 0.33 pg mL-1 for the detection of alpha fetoprotein. This study opens up a new avenue for the construction of electrochemical immunosensors with ultra-stable redox signal.

A highly sensitive label-free electrochemical immunosensor based on an aligned GaN nanowires array/polydopamine heterointerface modified with Au nanoparticles.

Aligned GaN nanowire arrays show great potential not only in optoelectronic devices, but also in sensitive biosensor applications, owing to their excellent chemical stability and biocompatibility, as well as high electron mobility and surface-to-volume ratio. However, to construct electrochemical immunosensors, proper surface modification of GaN nanowires, which can enable efficient charge transfer and provide large densities of immobilization sites for antibodies to anchor, is still challenging. Herein we demonstrate a highly sensitive label-free electrochemical immunosensing platform based on the integration of polydopamine (PDA) on a GaN nanowire surface. The PDA polymer was self-assembled on GaN nanowire surfaces via organic polymerization. The interface dipole layer generated at the GaN nanowire array/PDA polymer heterointerface enabled efficient charge transfer. The aligned GaN nanowire array/PDA hybrids were further modified with gold nanoparticles for subsequent covalent binding of antibodies. The fabricated immunosensor yielded a wide linear range between 0.01 and 100 ng ml-1 and a detection limit as low as 0.003 ng ml-1 for the detection of alpha-fetoprotein (AFP). The immunosensor showed good selectivity, reproducibility, and stability and was utilized in human serum samples for AFP detection. This work demonstrates the superiority of taking advantage of a nanowire array configuration and a semiconductor/polymer heterointerface in an immunosensing platform for sensitivity enhancement.