ZnO Transducers for Photoluminescence-Based Biosensors: A Review

Abstract

Zinc oxide (ZnO) is a wide bandgap semiconductor material that has been widely explored for countless applications, including in biosensing. Among its interesting properties, its remarkable photoluminescence (PL), which typically exhibits an intense signal at room temperature (RT), arises as an extremely appealing alternative transduction approach due to the high sensitivity of its surface properties, providing high sensitivity and selectivity to the sensors relying on luminescence output. Therefore, even though not widely explored, in recent years some studies have been devoted to the use of the PL features of ZnO as an optical transducer for detection and quantification of specific analytes. Hence, in the present paper, we revised the works that have been published in the last few years concerning the use of ZnO nanostructures as the transducer element in different types of PL-based biosensors, namely enzymatic and immunosensors, towards the detection of analytes relevant for health and environment, like antibiotics, glucose, bacteria, virus or even tumor biomarkers. A comprehensive discussion on the possible physical mechanisms that rule the optical sensing response is also provided, as well as a warning regarding the effect that the buffer solution may play on the sensing experiments, as it was seen that the use of phosphate-containing solutions significantly affects the stability of the ZnO nanostructures, which may conduct to misleading interpretations of the sensing results and unreliable conclusions.

Antibacterial Activity of Solvothermal Obtained ZnO Nanoparticles with Different Morphology and Photocatalytic Activity against a Dye Mixture: Methylene Blue, Rhodamine B and Methyl Orange

“…The visible emission bands from the fluorescence spectrum of ZnO are directly related to the presence of crystalline defects and are named deep level emission (DLE). In pure samples, a series of defects might exist: zinc vacancies (V Zn ), zinc interstitials (Zn i ), oxygen vacancies (V O ), oxygen interstitials (O i ), or oxygen anti-sites (O Zn ) [ 53 , 54 ]. The emission in the violet region is usually assigned to the V Zn while the blue emission (457 nm) is attributed to the transitions from Zn + I to valence band (VB).…”

Various Applications of ZnO Thin Films Obtained by Chemical Routes in the Last Decade

“…The properties of ZnO-based materials can be tailored and enhanced by controlling and optimizing several parameters (solution concentration [ 11 ], dopant level [ 12 , 13 ], synthesis [ 14 , 15 , 16 , 17 ], and annealing temperature [ 18 ] or pH [ 19 ]). In the last decade, the development of nanostructures with various morphologies [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ] such as: nanowires, nanorods (NR), nanoflowers, nanosheets, nanobelts, nanoneedles, nanoplates, has gained tremendous attention, being used in biological applications [ 8 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]: bioimaging, biosensing, antibacterial and drug delivery agents. In particular, ZnO thin films have optical (photoluminescence) [ 33 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ], electrical (thermoelectric [ 43 , 44 , 45 , 46 ], piezoelectric [ 47 , 48 , 49 , 50 , 51 , 52 , 53 ]) and biological (antimicrobial [ 54 , 55 , …”

Effect of Al Incorporation on the Structural and Optical Properties of Sol–Gel AZO Thin Films

“…[2]. In particular, ZnO thin films are used for the development of optoelectronic [3], transparent conductive oxides (TCOs) [4] and piezoelectric devices [5], photovoltaics [6], photocatalysts [7], gas sensors [8][9][10] or biosensors [11][12][13] due to their impressive optical (photoluminescence-PL) [14][15][16], electrical (thermoelectric, piezoelectric) [17][18][19][20] and biological (antimicrobial and antibacterial) [21][22][23] properties. It is well known that by doping, the aforementioned properties of ZnO thin films can be significantly improved.…”