Lab-on-nanopaper: A hand-held microfluidic sensing bioplatform based on curcumin nanoparticles embedded in bacterial nanopaper as an albumin assay kit

As a recent alternative to paper, bacterial cellulose (BC) nanopaper, as a sheet/film composed of continuous 3D network of nanosized cellulose fibers that are usually produced by specific nonpathogenic bacteria such as Acetobacterxylinum, due to having the optical transparency, high chemical, mechanical and thermal stability, low thermal expansion and surface roughness, and also the aforementioned advantageous properties of normal papers, provides an excellent substrate/platform for the development of optical (bio)sensors [1-5]. Herein, we introduce a microfluidic nanopaper-based analytical device (µ-NAD) or “lab-on-nanopaper” device for visual sensing of albumin in human blood serums, which relies on embedding of curcumin nanoparticles (NPs) within transparent bacterial cellulose (BC) nanopaper. Because of having the optical transparency and also the advantageous properties of normal papers including high flexibility, porosity, biodegradability and printability, BC nanopaper provides an excellent substrate/platform for the development of optical (bio)sensors. The hydrophilic test zones were created on the fabricated bioplatform through creating the hydrophobic walls via laser printing technology. The color changes of curcumin NPs embedded in BC nanopaper (CEBC) due to the inhibitory effect of human serum albumin (HSA) on the curcumin degradation in alkaline solutions, which can be monitored visually (naked eye/Smartphone camera) or spectroscopically using a spectrophotometer, were linearly proportional to the HSA concentration in the range of 10-300 µM and 25-400 µM, respectively. The developed µ-NAD/CEBC as a novel albumin assay kit was successfully utilized to the determination of HSA in human blood serum samples with satisfactory results. Building upon the fascinating features of BC nanopaper as a very promising bioplatform in optical (bio)sensing applications we are confident “lab-on-nanopaper” devices/µ-NADs, which integrate the advantages of the nanopaper with those of the microfluidics and also meet the ASSURED criteria, could be considered as a new generation of microfluidic based devices that are currently based on paper, glass or plastic substrates/platforms.