Role of Outer Surface Probes on Bullet-Shaped Asymmetric Solid-State Nanochannels for Lysozyme Protein Sensing.

Artificial solid-state nanochannels featuring precise partitions present a highly promising platform for biomarker detection. While the significance of probes on the outer surface (POS) has been relatively overlooked in the past, our research highlights their crucial role in biosensing. Furthermore, the contribution of POS on the bullet-shaped asymmetric nanochannels has not been extensively explored until now. Here, we fabricated a series of bullet-shaped nanochannels, each featuring a distinct asymmetric structure characterized by different tip- and base-pore diameters. These nanochannels were further modified with explicit distributions at the inner wall (PIW), the outer surface (POS), and their combination (POS + PIW) for lysozyme sensing. The impact of diameters, structural asymmetry, and surface charge density on the sensing efficacy of POS and PIW was thoroughly examined through experimental investigations and numerical simulations. POS demonstrates great individual sensing performance for lysozyme within a broad concentration range, spanning from 10 nM to 1 mM. Furthermore, it improves the sensitivity when combined with PIW, particularly within the nanochannels featuring the smaller base-pore diameter, resulting in a 2-fold increase in sensing performance for POS + PIW compared to PIW at a concentration of 10 nM. These findings are substantiated by numerical simulations that closely align with the experimental parameters. The contributions of POS are notably amplified in the presence of smaller base pores and a higher degree of asymmetry within the bullet-shaped nanochannels. These findings elucidate the mechanism underlying the role of POS within bullet-shaped asymmetric nanochannels and open up new avenues for manipulating and enhancing the sensing efficiency.

Polydopamine-Induced Modification on the Highly Charged Surface of Asymmetric Nanofluidics: A Strategy for Adjustable Ion Current Rectification Properties.

Surface charge effects in nanoconfines is one of the fundamentals in the ion current rectification (ICR) of nanofluidics, which provides entropic driving force by asymmetric surface charges and causes ion enrichment/depletion by the electrostatic interaction of fixed surface charges. However, the surface charge effect causes a significant electrostatic repulsion in nanoconfines, restricting additional like charge or elaborate chemistry on the highly charged confined surface, which limits ICR manipulation. Here, we use polydopamine (PDA), a nearly universal adhesive, that adheres to the highly positive-charged poly(ethyleneimine) (PEI) gel network in a nanochannel array. PDA enhances the ICR effect from a low rectification ratio of 9.5 to 92.6 by increasing the surface charge and hydrophobicity of the PEI gel network and, meanwhile, shrinking its gap spacing. Theoretical and experimental results demonstrate the determinants of the fixed surface charge in the enrichment/depletion region on ICR properties, which is adjustable by PDA-induced change in a nanoconfined environment. Chemically active PDA brings Au nanoparticles by chloroauric reduction for further hydrophobization and the modification of negative-charged DNA complexes in nanochannels, whereby ICR effects can be manipulated in versatile means. The results describe an adjustable and versatile strategy for adjusting the ICR behaviors of nanofluidics by manipulating local surface charge effects using PDA.

A wrinkled structure of gold film greatly improves the signaling of electrochemical aptamer-based biosensors.

Electrochemical aptamer-based (E-AB) sensors provide a great opportunity towards the goal of point-of-care and wearable sensing technologies due to their good sensitivity and selectivity. Nevertheless, the output signals from this sensor class remain low when sensors are interrogated via square-wave voltammetry. This low signaling limits the sensor's precision for its capability to detect small changes in target concentrations. To circumvent this, we proposed here the use of a readily shrink-induced, wrinkled Au-coating polyolefin film to immobilize a greater number of DNA probes and thus improve the signaling. Specifically, wrinkled gold film exhibits a 5.5-fold increase of surface area in comparison to the unwrinkled ones. Using these substrates we fabricated a set of E-AB sensors of three biological molecules, including kanamycin, doxorubicin and ATP. We achieved up to 10-fold increase in its current and also good accuracies within ±20% error in the target concentration range across 2 orders of magnitude.