Abstract
Soft, deformable, molecularly imprinted nanoparticles (nanoMIPs) were combined to nano-plasmonic sensor chips realized on poly (methyl methacrylate) (PMMA) substrates to develop highly sensitive bio/chemical sensors. NanoMIPs (dmean < 50 nm), which are tailor-made nanoreceptors prepared by a template assisted synthesis, were made selective to bind Bovine Serum Albumin (BSA), and were herein used to functionalize gold optical nanostructures placed on a PMMA substrate, this latter acting as a slab waveguide. We compared nanoMIP-functionalized non-optimized gold nanogratings based on periodic nano-stripes to optimized nanogratings with a deposited ultra-thin MIP layer (<100 nm). The sensors performances were tested by the detection of BSA using the same setup, in which both chips were considered as slab waveguides, with the periodic nano-stripes allocated in a longitudinal orientation with respect to the direction of the input light. Result demonstrated the nanoMIP-non optimized nanogratings showed superior performance with respect to the ultra-thin MIP-optimized nanogratings. The peculiar deformable character of the nano-MIPs enabled to significantly enhance the limit of detection (LOD) of the plasmonic bio/sensor, allowing the detection of the low femtomolar concentration of analyte (LOD ∼ 3 fM), thus outpassing of four orders of magnitude the sensitivies achieved so far on optimized nano-patterned plasmonic platforms functionalized with ultra-thin MIP layers. Thus, deformable nanoMIPs onto non-optimized plasmonic probes permit to attain ultralow detections, down to the quasi-single molecule. As a general consideration, the combination of more plasmonic transducers to different kinds of MIP receptors is discussed as a mean to attain the detection range for the selected application field.
Highlights
Optical sensors hold great potential in the bioanalytical field, finding increasing point-of-care (POC), and Internet-ofthings (IoT) applications
Earlier in our group, we demonstrated that an Surface Plasmon Resonance (SPR) probe based on a PMMA slab waveguide for the detection of furfural and using a specific molecularly imprinted polymers (MIPs) receptor layer, having a thickness of about 700 nm (Zeni et al, 2018) has an overall performance similar to that obtained for the transducer being an SPR D-shaped Plastic Optical Fiber (POF) sensor functionalized with the same MIP layer (Cennamo et al, 2011)
In the experimental setup we considered the PMMA substrate of the nanoplasmonic chip as a transparent substrate, onto which the periodic nano-stripes were allocated in a longitudinal orientation with respect to the direction of the input light
Summary
Optical sensors hold great potential in the bioanalytical field, finding increasing point-of-care (POC), and Internet-ofthings (IoT) applications. Optical sensors integrated on silicon-based substrates find uses in gas sensing (Siebert and Müller, 2005; Airoudj et al, 2008; Huang et al, 2014; Consani et al, 2018; Maurya et al, 2018), magnetic field sensing (Deghdak et al, 2017; Ge et al, 2021), detection of biological, and chemical species (Densmore et al, 2007; Mukundan et al, 2009; Schmitt et al, 2011; Kozma et al, 2014; Kumar et al, 2021) These sensors offer all the advantages of the technological and fabrication processes typical of the microelectronic industry, such as the integration with other components, the low-cost, and the small-size of the produced device. We proposed a multimode slab waveguide based on a poly (methyl methacrylate) (PMMA) substrate and intended for the realization of plasmonic biosensors with a very simple experimental setup This PMMA chip has been showing to perform as an SPR sensor, as reported in (Cennamo et al, 2017). The state of art of MIP-based photonic structures has been recently discussed (Chiappini et al, 2020)
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