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Friday, 05 December 2014

Paper and plastic-based nanobiosensors are a new green technology for biosensors fabrication

Researchers from the ICN2 Nanobioelectronics and Biosensors Group, led by the ICREA research Prof Arben Merkoci, have an active scientific production in paper/plastic-based nanobiosensors. Four recent works in Lab Chip, Analytical Chemistry and Nano Research summarize their recent activity in the field.

Paper-based biosensing technology is emerging as a new green technology for biosensors fabrication. Paper, this green and low cost material combined with the use of nanomaterials and nanotechnologies is bringing new opportunities in the field of nanobiosensors design and fabrication. Paper-microfluidics, a zero-energy platform, can be easily integrated with various biological receptors (i.e. antibodies, DNA strands) modified with nanoparticles in the so called lateral-flow assays (LFA). Although LFAs are widely used in some point of care applications (POC) they can't still be extended to several other POCs where higher sensitivities and lower detection limits are required.

To overcome such a drawback, researchers from the ICN2 Nanobioelectronics and Biosensors Group, led by the ICREA research Prof Arben Merkoci, developed a simple and facile to be implemented alternative that improves the sensitivity of LFA. This is based on the use of delay hydrophobic barriers fabricated by using wax-printing technique. [1] Several wax pillars patterns were printed onto nitrocellulose membrane in order to produce delays as well as pseudo turbulences into the microcapillary flow. The proposed wax pillar modified devices were tested for detection of HIgG as model protein in a gold nanoparticle-based LFA, showing a sensitivity improvement of almost 3-fold in comparison to a conventional free-barrier LFA.

While this nanoparticle-based LFA is convenient for application of low volumes of samples its applicability in cases where large volume of samples are requested to be tested is rather limited. To overcome this drawback ICN2 researchers developed an innovative 'Lab-in-a-syringe' (LIS) based on the same LFA concept but operating in 'vertical-flow' mode using paper platforms and gold nanoparticles. [2] This simple diagnostic device features simultaneous sampling and vertical-flow operation, meaning that unlike typical immunosensors, it does not suffer from any delay between sampling and detection. It can handle large-volume, low-concentration samples for sample analysis in diverse applications (e.g. biomedical, environmental, food, etc.). Furthermore, its operating range for sample concentration can be tuned by simply changing the volume of the syringed sample, which enables on-demand limits of detection (LOD).

The LIS contains two nitrocellulose pads: the conjugate pad (which captures the analyte) and the detection pad (which signals the presence of the captured analyte) both embedded into reusable plastic cartridges. We demonstrated its efficiency at detecting IgG (LOD: 1.0 ng/mL) and prostate-specific antigen (PSA) (spiked urine samples; LOD: 1.9 ng/mL). In the field the LIS can be used for complete on-site analysis, or to obtain partially analyzed samples (AuNPs with captured analyte) for subsequent detailed testing in specialized laboratories.

The performance of paper-based bioelectronics sensors is strongly related with the development of stable reference electrode. This is why the group developed recently a miniaturized, disposable and low cost Ag/AgCl pseudo-reference electrode based on inkjet printing. [3] Silver ink was printed and afterwards chlorinated with bleach solution. The reference electrodes obtained in this work showed a good reproducibility and stability during at least 30 min continuous measurement and even after 30 days stored without special care. Moreover, the strategy used can be useful for large scale production of solid-state Ag/AgCl pseudo-reference electrode with different designs and sizes, facilitating the coupling with different electrical/electrochemical micro-sensors and biosensors.

Beside paper-based platforms, flexible sensors are getting an increased interest due to their low cost combined with a variety of architectures that can be easily integrated in the same platform. This is the case of a disposable and single-use assembled nanoparticles-based nanochannel platform onto a flexible substrate for label-free immunosensing developed in collaboration with researchers in EMPA (Switzerland). [4] This sensing platform is formed by the dip-coating of a homogeneous and assembled monolayer of carboxylated polystyrene nanospheres (PS, 200 nm and 500 nm-sized) onto the working area of flexible screen-printed ITO/PET electrodes. The spaces between the self-assembled nanospheres generate well-ordered nanochannels, with inter-PS particles distances of around 65 and 24 nm respectively. The formed nanochannels are approached for the effectively immobilization of antibodies and subsequent protein detection based on the monitoring of [Fe(CN)6]4- flow through diffusion and the decrease in the differential pulse voltammetric (DPV) signal upon immunocomplex formation.

The obtained sensing system is nanochannel-size dependent and allows to detect human IgG (chosen as model analyte) at levels of 580 ng/mL. The developed device represents an integrated and simple biodetection system which overcomes many of the limitations of previously reported nanochannels-based approaches and can be extended in the future to several other immuno and DNA detection systems.

Published papers:

[1] Lourdes Rivas, Mariana Medina-Sanchez, Alfredo de la Escosura-Muniz, Arben Merkoci. Improving sensitivity of gold nanoparticle-based lateral flow assays by using wax-printed pillars as delay barriers of microfluidics. Lab Chip, 2014; 14:4406-4414. http://pubs.rsc.org/en/content/articlelanding/2014/lc/c4lc00972j#!divAbstract [2] Gisele Elias Nunes Pauli, Alfredo de la Escosura-Muniz, Claudio Parolo,a Ivan Helmuth Bechtold, Arben Merkoci. Lab-in-a-syringe using gold nanoparticles for rapid immunosensing of protein biomarkers. Lab Chip, 2015; Advance Article, DOI: 10.1039/C4LC01123F. http://pubs.rsc.org/en/content/articlelanding/2014/lc/c4lc01123f#!divAbstract [3] Everson T. S. G. da Silva , Sandrine Miserere , Lauro T. Kubota , and Arben Merkoci, Simple on-plastic/paper inkjet-printed solid- state Ag/AgCl pseudo-reference electrode, Analytical Chemistry, 2014. 86 (21); 10531–10534. http://pubs.acs.org/doi/abs/10.1021/ac503029q [4] Alfredo de la Escosura-Muniz, Marisol Espinoza-Castaneda, Madoka Hasegawa, Laetitia Philippe, Arben Merkoci. Assembled nanoparticles-based nanochannels onto a plastic flexible substrate for label-free immunosensing. Nano Research. Just accepted Manuscript, October 2014. DOI 10.1007/s12274-014-0598-5 http://www.thenanoresearch.com/upload/justPDF/0598.pdf