Socio-economic demands and challenges for non-invasive disease diagnosis through a portable breathalyzer by the incorporation of 2D nanosheets and SMO nanocomposites

Boosting Gaseous Acetone Detection by Nanoheterojunctions of p-Type MWCNTs/PANI Integrated into 3D Flame-Synthesized n-Type ZnO

Accurate methods for detecting volatile organic compounds (VOCs) are essential for noninvasive disease diagnosis, with breath analysis providing a simpler, user-friendly alternative to traditional diagnostic tools. However, challenges remain in low-temperature VOC solid-state sensors, especially concerning their selectivity and functionality at room temperature. Herein, we present key insights into optimizing multiwalled carbon nanotubes (MWCNTs)/polyaniline (PANI) and ZnO nanocomposites for efficient, light-free selective acetone sensing. We showcased novel nanocomposites prepared by integrating p-type MWCNTs/PANI into a porous 3D network of n-type ZnO nanoparticles, synthesized via flame spray pyrolysis, and varying the weight ratios between ZnO and MWCNTs/PANI (namely 1:1, 8:1, 32:1, 64:1). The 32:1 nanocomposite exhibited superior acetone selectivity over toluene and ethanol, resulting in promise even at room temperature. As such, a potential sensing mechanism was proposed, which involves nanoheterojunction formation between p-type MWCNTs/PANI and n-type ZnO, creating an accumulation layer that enhances the gas response. Moreover, the incorporation of MWCNTs improved the overall conductivity and carrier mobility. Hence, we believe that this work offers valuable insights for optimizing MWCNTs/PANI and ZnO nanocomposites for efficient, low-temperature, light-free gas sensors.

Gold nanocluster-based fluorescent sensors for in vitro and in vivo ratiometric imaging of biomolecules

Gold nanoclusters (AuNCs) are promising nanomaterials for ratiometric fluorescent probes due to their tunable fluorescence wavelengths dependent on size and structure, as well as their biocompatibility and resistance to photobleaching. By incorporating an additional fluorescence spectral peak, dual-emission AuNC-based fluorescent probes have been developed to enhance the signal output reproducibility. These probes can be fabricated by integrating various luminescent nanomaterials with AuNCs. This review focuses on the preparation methods and applications of ratiometric fluorescent probes derived from AuNCs and other fluorescent nanomaterials or fluorescent dyes for both in vitro and in vivo bioimaging of target analytes. Additionally, the review delves into the sensing mechanisms of AuNC-based ratiometric probes, their synthetic strategies, and the challenges encountered when using AuNCs for ratiometric bioimaging. Moreover, we explore the application of protein-stabilized AuNCs and thiolate-capped AuNC-based ratiometric fluorescent probes for biosensing and bioimaging. Two primary methods for assembling AuNCs and fluorophores into ratiometric fluorescent probes are discussed: triggered assembly and self-assembly. Finally, we address the challenges and issues associated with ratiometric bioimaging using AuNCs and propose future directions for further advancing AuNCs as ratiometric imaging agents.

The Role of Nano-Sensors in Breath Analysis for Early and Non-Invasive Disease Diagnosis

Early-stage, precise disease diagnosis and treatment has been a crucial topic of scientific discussion since time immemorial. When these factors are combined with experience and scientific knowledge, they can benefit not only the patient, but also, by extension, the entire health system. The development of rapidly growing novel technologies allows for accurate diagnosis and treatment of disease. Nanomedicine can contribute to exhaled breath analysis (EBA) for disease diagnosis, providing nanomaterials and improving sensing performance and detection sensitivity. Through EBA, gas-based nano-sensors might be applied for the detection of various essential diseases, since some of their metabolic products are detectable and measurable in the exhaled breath. The design and development of innovative nanomaterial-based sensor devices for the detection of specific biomarkers in breath samples has emerged as a promising research field for the non-invasive accurate diagnosis of several diseases. EBA would be an inexpensive and widely available commercial tool that could also be used as a disease self-test kit. Thus, it could guide patients to the proper specialty, bypassing those expensive tests, resulting, hence, in earlier diagnosis, treatment, and thus a better quality of life. In this review, some of the most prevalent types of sensors used in breath-sample analysis are presented in parallel with the common diseases that might be diagnosed through EBA, highlighting the impact of incorporating new technological achievements in the clinical routine.

Interfacial Ammonia Selectivity, Atmospheric Passivation, and Molecular Identification in Graphene-Nanopored Activated Carbon Molecular-Sieve Gas Sensors

Graphene's inherent nonselectivity and strong atmospheric doping render most graphene-based sensors unsuitable for atmospheric applications in environmental monitoring of pollutants and breath detection of biomarkers for noninvasive medical diagnosis. Hence, demonstrations of graphene's gas sensitivity are often in inert environments such as nitrogen, consequently of little practical relevance. Herein, target gas sensing at the graphene-activated carbon interface of a graphene-nanopored activated carbon molecular-sieve sensor obtained via the postlithographic pyrolysis of Novolac resin residues on graphene nanoribbons is shown to simultaneously induce ammonia selectivity and atmospheric passivation of graphene. Consequently, 500 parts per trillion (ppt) ammonia sensitivity in atmospheric air is achieved with a response time of ∼3 s. The similar graphene and a-C workfunctions ensure that the ambipolar and gas-adsorption-induced charge transfer characteristics of pristine graphene are retained. Harnessing the van der Waals bonding memory and electrically tunable charge-transfer characteristics of the adsorbed molecules on the graphene channel, a molecular identification technique (charge neutrality point disparity) is developed and demonstrated to be suitable even at parts per billion (ppb) gas concentrations. The selectivity and atmospheric passivation induced by the graphene-activated carbon interface enable atmospheric applications of graphene sensors in environmental monitoring and noninvasive medical diagnosis.