Microneedles (MNs) are an emerging technology in pharmaceutics and biomedicine, and are ready to be commercialized in the world market. However, solid microneedles only allow small doses and time-limited administration rates. Moreover, some well-known and already approved drugs need to be re-formulated when supplied by MNs. Instead, hollow microneedles (HMNs) allow for rapid, painless self-administrable microinjection of drugs in their standard formulation. Furthermore, body fluids can be easily extracted for analysis by a reverse use of HMNs, thus making them perfect for sensing issues and theranostics applications. The fabrication of HMNs usually requires several many-step processes, increasing the costs and consequently decreasing the commercial interest. Photolithography is a well-known fabrication technique in microelectronics and microfluidics that fabricates MNs. In this paper, authors show a proof of concept of a patented, easy and one-shot fabrication of two kinds of HMNs: (1) Symmetric HMNs with a “volcano” shape, made by using a photolithographic mask with an array of transparent symmetric rings; and (2) asymmetric HMNs with an oblique aperture, like standard hypodermic steel needles, made by using an array of transparent asymmetric rings, defined by two circles, which centers are slightly mismatched. Simulation of light propagation, fabrication process, and preliminary results on ink microinjection are presented.

Current advances in the fabrication of smart nanomaterials and nanostructured surfaces find wide usage in the biomedical field. In this context, nanosensors based on localized surface plasmon resonance exhibit unprecedented optical features that can be exploited to reduce the costs, analytic times, and need for expensive lab equipment. Moreover, they are promising for the design of nanoplatforms with multiple functionalities (e.g., multiplexed detection) with large integration within microelectronics and microfluidics. In this review, we summarize the most recent design strategies, fabrication approaches, and bio-applications of plasmonic nanoparticles (NPs) arranged in colloids, nanoarrays, and nanocomposites. After a brief introduction on the physical principles behind plasmonic nanostructures both as inherent optical detection and as nanoantennas for external signal amplification, we classify the proposed examples in colloid-based devices when plasmonic NPs operate in solution, nanoarrays when they are assembled or fabricated on rigid substrates, and nanocomposites when they are assembled within flexible/polymeric substrates. We highlight the main biomedical applications of the proposed devices and offer a general overview of the main strengths and limitations of the currently available plasmonic nanodevices.

Over the last 30 years, optical biosensors based on nanostructured materials have obtained increasing interest since they allow the screening of a wide variety of biomolecules with high specificity, low limits of detection, and great sensitivity. Among them, flexible optical platforms have the advantage of adapting to non-planar surfaces, suitable for in vivo and real-time monitoring of diseases and assessment of food safety. In this review, we summarize the newest and most advanced platforms coupling optically active materials (noble metal nanoparticles) and flexible substrates giving rise to hybrid nanomaterials and/or nanocomposites, whose performances are comparable to the ones obtained with hard substrates (e.g., glass and semiconductors). We focus on localized surface plasmon resonance (LSPR)-based and surface-enhanced Raman spectroscopy (SERS)-based biosensors. We show that large-scale, cost-effective plasmonic platforms can be realized with the currently available techniques and we emphasize the open issues associated with this topic.

A 3D plasmonic sensing platform that combines the properties of citrate gold nanoparticles (AuNPs) and poly-(ethylene glycol) diacrylate (PEGDA) hydrogels is proposed as a nanocomposite hybrid material for biosensing applications, whose optical properties and sensitivity can be tuned by varying the particle mean diameter as also predicted by the Mie theory. It is found that AuNPs embedded in the hydrogel network are more stable when compared to the colloidal aqueous solutions. PEGDA hydrogel physically retains the gold nanoparticles even after a full swelling process during immersion in liquids. Such a property is confirmed by exposing the AuNPs-containing PEGDA hydrogels to organic solvents and buffers that would usually cause the aggregation of the nanoparticles in solution. Moreover, biotin, as a small molecule model, has been captured, and optically detected with a transmission mode customized setup, by a cysteamine modified AuNPs-containing PEGDA hydrogel layer to achieve a biorecognition hybrid device.

Interstitial fluid (ISF) extraction and analysis are challenges that can be tackled by Hollow MicroNeedles (HMNs) technology, overcoming most of the difficulties associated with in situ detection. Herein, a plasmonic transducer, composed of gold nanoparticles embedded in poly(ethylene glycol) diacrylate (PEGDA) hydrogels, is integrated in the inner cavity of HMNs to detect biomarkers from the ISF‐based point‐of‐care. The wearable HMN‐based patch is used for minimally invasive pierce of the skin. The large swelling capability of the plasmonic transducer allows the uptake of ISF by capillarity. Biotin, as a small model molecule, is efficiently collected in the inner cavity of HMN and its high specificity with the streptavidin is exploited as a validation of the plasmonic nanocomposite functionality embedded within. The recognition of biotin is achieved in dual‐optical mode: the localized surface plasmon resonance (label‐free) and the metal‐enhanced fluorescence (label‐based). Overall, the proposed HMN‐based patch for target sensing in ISF can represent a novel point‐of‐use device for the detection of biomarkers as an alternative to conventional hospital or lab settings to help faster medical decision‐making.