Search

Biosensors play a critical role in modern diagnostics, offering high sensitivity and specificity for detecting various relevant clinical analytes as well as real-time monitoring and integrability in point-of-care (POC) platforms and wearable/implantable devices. Among the numerous materials used as biosensing substrates, porous silicon (pSi) has garnered significant attention due to its tunable properties, ease of fabrication, large surface area, and versatile surface chemistry. These attributes make pSi an ideal platform for transducer development, particularly in the fabrication of optical and electrochemical biosensors. This review explores the various stages of the design of a pSi-based biosensor starting from pSi fabrication, followed by a deep study about the stabilization and functionalization techniques providing a comparative analysis of their performance. Moreover, we survey the reported designs categorized as optical and electrochemical sensors, presenting a critical evaluation of their analytical validity as well as identifying the challenges of bringing these devices to the clinical practice. By bridging existing knowledge gaps, this review aims to inspire future innovation, providing valuable insights into how pSi-based biosensors can be further optimized for noninvasive diagnostics, personalized healthcare, and early disease detection leading to a doable commercialization.

Microneedles (MNs) or microneedle arrays (MNAs) are critical components of minimally invasive devices comprised of a single or a series of micro-scale projections. MNs can bypass the outermost layer of the skin and painlessly access microcirculation of the epidermis and dermis layers, attracting great interest in the development of personalized healthcare monitoring and diagnostic devices. However, MN technology has not yet reached its full potential since current micro- and nanofabrication methods do not address the need of fabricating MNs with complex surfaces to facilitate the development of clinically adequate devices. This work presents a new approach that combines 3D printing technology based on two-photon polymerization with soft lithography for cost-effective and time-saving fabrication of complex MNAs. Specifically, this method relies on printing complex 3D objects efficiently replicated into polymeric substrates via soft lithography, resulting in a free-standing polymeric lattice (PL) membrane that can be transferred onto gold-coated MNs and used for electrochemical biosensing. This platform shows excellent electrochemical performance in detecting metabolite (glucose) and protein (insulin) biomarkers with a dynamic linear range sufficient for detecting biomarkers in healthy individuals and patients. The approach holds great potential for fabricating next-generationMNs, including their transfer into clinically adequate devices., (© 2024 Wiley‐VCH GmbH.)

A major societal challenge is the development of the necessary tools for early diagnosis of diseases such as cancer and sepsis. Consequently, there is a concerted push to develop low-cost and non-invasive methods of analysis with high sensitivity and selectivity. A notable trend is the development of highly sensitive methods that are not only amenable for point-of-care (POC) testing, but also for wearable devices allowing continuous monitoring of biomarkers. In this context, a non-invasive test for the detection of a promising biomarker, the protein Interleukin-6 (IL-6), could represent a significant advance in the clinical management of cancer, in monitoring the chemotherapy response, or for prompt diagnosis of sepsis. This work reports a capacitive electrochemical impedance spectroscopy sensing platform tailored towards POC detection and treatment monitoring in human serum. The specific recognition of IL-6 was achieved employing gold surfaces modified with an anti-IL6 nanobody (anti-IL-6 VHH) or a specific IL-6 aptamer. In the first system, the anti-IL-6 VHH was covalently attached to the gold surface using a binary self-assembled-monolayer (SAM) of 6-mercapto-1-hexanol (MCH) and 11-mercaptoundecanoic acid. In the second system, the aptamer was chemisorbed onto the surface in a mixed SAM layer with MCH. The analytical performance for each label-free sensor was evaluated in buffer and 10% human serum samples and then compared. The results of this work were generated using a low-cost, thin film eight-channel gold sensor array produced on a flexible substrate providing useful information on the future design of POC and wearable impedance biomarker detection platforms., (© 2023. The Author(s).)

The prostate specific antigen (PSA) test is the gold standard for the screening of prostate cancer (PCa), despite its limited clinical specificity. Long noncoding RNAs are released from the tumor tissue to the urine and show great potential for improving specificity in PCa diagnosis. This work reports on a sandwich-type hybridization assay to detect both the urinary biomarker prostate cancer antigen 3 (PCA3) and an endogenous control, the PSA mRNA. Multiple fluorescein-tagged hybridization assistant probes are used to promote the selective capture of this long noncoding RNA, and sensitivity by incorporating multiple redox enzymes per target molecule, after addition of antifluorescein Fab fragment-peroxidase conjugate. This strategy alleviates the problems associated with the low natural abundance of this marker, its large size, and complex secondary structure. The individual genosensors exhibit good sensitivity (2.48 ± 0.01 μA nM -1 and 6.4 ± 0.3 μA nM -1 for PCA3 and PSA, respectively), with wide linear ranges (from 25 pM to 10 nM for PCA3 and 1 nM for PSA), and detection limits in the low picomolar range (4.4 pM and 1.5 pM for PCA3 and PSA, respectively). This analytical performance is retained in the dual configuration without significant cross-talk, despite using the same enzyme label. The usefulness of this dual platform was demonstrated by analyzing RNA extracts from the prostate cancer cell line LNCaP and from urine samples of prostate cancer patients., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)

Genosensing technology has mostly based on mixed self-assembled monolayers (SAMs) of thiol-modified oligonucleotides and alkanethiols on gold surfaces. However, the typical backfilling approach, which incorporates the alkanethiol in a second step, gives rise to a heterogeneous distribution of oligonucleotide probes on the surface, negatively affecting to both hybridization efficiency and surface stability. Despite aromatic thiols present a remarkably different behavior from alkanethiols, with higher rigidity and stronger intermolecular interactions, they have been scarcely explored for the fabrication of DNA sensing platforms. We have investigated different approaches involving SAMs of aromatic thiols, namely p-mercaptobenzoic acid (p-MBA) and p-aminothiophenol (p-ATP), to yield DNA sensing layers for sequence-specific detection of target oligonucleotides. The studied monolayers were evaluated by DNA surface coverage and further information was obtained by determining their functionality in a sandwich hybridization assay with enzymatic amplification of the electrochemical read-out. The insertion of thiol-oligonucleotides into p-ATP monolayers previously oxidized, and the covalent binding of amino-oligonucleotides to pure p-MBA monolayers give rise to increased storage stability and better analytical performance. The quantification of RNA from Legionella pneumophila cellular lysates was successfully performed, illustrating the usefulness of these sensing architectures for detecting pathogenic bacteria., (Copyright © 2017 Elsevier B.V. All rights reserved.)