After over 30 years of development, surface-enhanced Raman spectroscopy (SERS) is now facing a very important stage in its history. The explosive development of nanoscience and nanotechnology has assisted the rapid development of SERS, especially during the last 5 years. Further development of surface-enhanced Raman spectroscopy is mainly limited by the reproducible preparation of clean and highly surface enhanced Raman scattering (SERS) active substrates. This review deals with some substrate-related issues. Various methods will be introduced for preparing SERS substrates of Ag and Au for analytical purposes, from SERS substrates prepared by electrochemical or vacuum methods, to well-dispersed Au or Ag nanoparticle sols, to nanoparticle thin film substrates, and finally to ordered nanostructured substrates. Emphasis is placed on the analysis of the advantages and weaknesses of different methods in preparing SERS substrates. Closely related to the application of SERS in the analysis of trace sample and unknown systems, the existing cleaning methods for SERS substrates are analyzed and a combined chemical adsorption and electrochemical oxidation method is proposed to eliminate the interference of contaminants. A defocusing method is proposed to deal with the laser-induced sample decomposition problem frequently met in SERS measurement to obtain strong signals. The existing methods to estimate the surface enhancement factor, a criterion to characterize the SERS activity of a substrate, are analyzed and some guidelines are proposed to obtain the correct enhancement factor.
Respiration monitoring
is important for evaluating human health.
Humidity sensing is a promising way to establish a relationship between
human respiration and electrical signal. This work describes polymer
humidity sensors with ultrafast response for respiration monitoring.
The humidity-sensitive polyelectrolyte is in situ cross-linked on the substrate printed with interdigitated electrodes
by a thiol–ene click reaction. The polyelectrolyte humidity
sensor shows rapid water adsorption/desorption ability, excellent
stability, and repeatability. The sensor with ultrafast response and
recovery (0.29/0.47 s) when changing humidity between 33 and 95% shows
good application prospects in breath monitoring and touchless sensing.
Different respiration patterns can be distinguished, and the breath
rate/depth of detection subjects can also be determined by the sensor.
In addition, the obtained sensor can sense the skin evaporation in
a noncontact way.
SummaryThe development of novel DNA sequencing methods is one of the ongoing challenges in various fields of research seeking to address the demand for sequence information. However, many of these techniques rely on some kind of labeling or amplification steps. Here we investigate the intrinsic properties of tip-enhanced Raman scattering (TERS) towards the development of a novel, label-free, direct sequencing method. It is known that TERS allows the acquisition of spectral information with high lateral resolution and single-molecule sensitivity. In the presented experiments, single stranded adenine and uracil homopolymers were immobilized on different kinds of substrates (mica and gold nanoplates) and TERS experiments were conducted, which demonstrated the reproducibility of the technique. To elucidate the signal contributions from the specific nucleobases, TERS spectra were collected on single stranded calf thymus DNA with arbitrary sequence. The results show that, while the Raman signals with respect to the four nucleobases differ remarkably, specific markers can be determined for each respective base. The combination of sensitivity and reproducibility shows that the crucial demands for a sequencing procedure are met.
TERS (tip-enhanced Raman scattering) provides exceptional spatial resolution without any need for labelling and has become a versatile tool for biochemical analysis. Two examples will be highlighted here. On the one hand, TERS measurements on a single mitochondrion are discussed, monitoring the oxidation state of the central iron ion of cytochrome c, leading towards a single protein characterization scheme in a natural environment. On the other hand, a novel approach of single molecule analysis is discussed, again based on TERS experiments on DNA and RNA, further highlighting the resolution capabilities of this method.
Flexible
temperature sensors with high resolution and good reliability
under deformation are a major research focus for wearable electronic
devices for skin temperature monitoring. In this study, a fiber-like
temperature sensor is fabricated by in situ growing poly(3,4-ethylenedioxythiophene)
(PEDOT) on the surface of thermoplastic polyurethane (TPU) fiber.
The temperature sensor achieves a high sensitivity of 0.95%·°C–1 with a high linearity between 20
and 40 °C. Most importantly, the sensor achieves a high temperature
resolution of 0.2 °C. Due to its structure, the temperature-sensitive
fiber is easily embedded into textiles. By sewing the fiber into normal
textiles in an S-shape, the interference of strain can be nearly avoided,
even when the textile is stretched to 140%. Also, the obtained sensors
can monitor skin temperature during exercise, which demonstrates the
potential of the sensor’s application in healthcare and disease
diagnosis.
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