Synthesis approaches to colloidal Cu₃P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump–probe measurements on platelet-shaped Cu_3-xP NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu₃P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu_3-xP NCs. It is likely that both the LSPR and the p-type character of our Cu_3-xP NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu_3-xP NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu_3-xP NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu_3-xP is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu_3-xP/InP heterostructures, as a consequence of the fact that the exchange between Cu⁺ and In³⁺ ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu_3-xP NCs an interesting material platform from which to access other metal phosphides by cation exchange.

In many applications of near-infrared (NIR) light detection, a band-pass filter is needed to exclude the noise caused by visible light. Here, we demonstrate a filterless, visible-blind, narrow-band NIR photodetector with a full-width at half-maximum of 4 μm) nanocomposite absorbing layers made of polymer–fullerene:lead sulfide (PbS) quantum dots (QDs). The PbS QDs yield a photoconductive gain due to their hole-trapping effect, which effectively enhances both the responsivity and the visible rejection ratio of the external quantum efficiency by >10 fold compared to those without PbS QDs. Encouragingly, the inclusion of the PbS QDs does not increase the device noise. We directly measured a noise equivalent power (NEP) of 6.1 pW cm⁻² at 890 nm, and a large linear dynamic range (LDR) over 11 orders of magnitude. The highly sensitive visible-blind NIR narrow-band photodetectors may find applications in biomedical engineering.

We demonstrate controllable fabrication of Ag nanoparticle (NP)-decorated reduced graphene oxide (RGO/Ag) hybrids and their application for fast and selective detection of ammonia at room temperature. Ag NPs greatly improved the sensitivity of RGO. The response time (6 s) and recovery time (10 s) are comparable with our previous Ag NP-decorated multiwalled carbon nanotube (MWCNT/Ag) NH₃ sensors; however, the sensitivity is about twice that of MWCNT/Ag hybrids. We found that the loading density of NPs greatly affects the sensing performance of RGO/Ag hybrids and a proper NP loading leads to maximum sensitivity.

Due to potential risks to the environment and human health arising from pathogens/chemical contaminants, novel devices are being developed for rapid and precise detection of those contaminants. Here, we demonstrate highly sensitive and selective field-effect transistor (FET) sensor devices for detection of Escherichia coli (E. coli) bacteria using thermally reduced monolayer graphene oxide (TRMGO) sheets as semiconducting channels. The graphene oxide (GO) sheets are assembled on the aminoethanethiol (AET)-functionalized gold (Au) electrodes through electrostatic interactions with ultrasonic assistance. Anti-Escherichia coli (anti-E. coli) antibodies are used as receptors for selective detection of E. coli cells and integrated on the FET device through covalent bonding with Au nanoparticles on the GO surface. The TRMGO FET device shows great electronic stability and high sensitivity to E. coli cells with a concentration as low as 10 colony-forming units (cfu) per mL. The biosensing platform reported here is promising for large-scale, sensitive, selective, low-cost, and real-time detection of E. coli bacteria.