Study On Electrochemiluminescence Of Eu³⁺-doped CdS Nanocrystals And Their Analytical Application

Electrogenerated chemilumiescence(ECL)is an analytical method combining electrochemistry with chemilumiescence.This technology has been extensively used in many domains owing to its advantages such as higher sensitivity,the potential control over the ECL reaction,without expensive instruments.Semiconductor nanocrystals(SNCs)with excellent luminescent properties and good biocompatibilities have extensively applied in biolabel and biosensing fields.Resonance energy transfer is a new molecular spectroscopy method,referring to the transfer of electronic excitation energy from the appropriate energy donors to receptors.Electrochemiluminescence resonance energy transfer(ECL-RET),which combines the advantages of both,is a new area with great development potential and has been widely used in the construction of biosensors.Here,we try to develop new ECL-RET donor-receptor pairs to build sensitive biosensors.Based on the current developments of SNCs ECL and biosensors in our group,in this thesis,through the development of novel doped SNCs and fabrication of innovative ECL system and the exploitation of ingenious signaling mechanism,we established three advanced methods in ECL bioanalysis.The major contents were described as follows:1.Electrochemiluminescence behaviors of Eu3+-doped CdS nanocrystals film in aqueous solutionEu3+ doped CdS nanocrystals(CdS:Eu NCs)were synthesized via co-precipitation method.The doping of Eu3+ ions caused a 4-fold enhancement in ECL intensity and more stable cathodic signals compared to pure CdS NCs.Such enhancement was mostly ascribed to doping-induced improvement in the stability of reduced NCs and the energy transfer from host NCs to Eu3+ ions on the surface to decrease the non-radiative transition probability.A new emission peak around 620 nm was observed in ECL spectra of the doped NCs,which belonged to the 5D→7F2 transition of Eu3+ ions in CdS NCs.Correspondingly,a pair of oxidation and reduction peaks occurred at+1.01 V and +0.61 V because of the formation of Eu3+-surface states complex when the CdS:Eu NCs solution underwent cyclic voltammogram scanning.Benefiting from the strong ECL emission of the doped NCs and high affinity of the doped Eu3+ ions to oxygen,CdS:Eu NCs film showed a great oxygen-sensitivity.The intense red luminescence of the characteristic transitions of Eu3+ in CdS:Eu NCs would also have enormous potential in bioanlytical system.2.An off-on-off electrochemiluminescence approach for ultrasensitive detection of thrombinAn aptasensor for ultrasensitive ECL detection of thrombin was constructed based on an "off-on-off" approach.The system is composed of a CdS:Eu NCs film on glassy carbon electrode(GCE)as ECL emitter.Then gold nanoparticles(AuNPs)labeled hairpin-DNA probe(ssDNAl)containing thrombin-binding aptamer(TBA)sequence was linked on the NCs film,which led to an ECL quenching(off)as a result of Forster-resonance energy transfer(FRET)between the CdS:Eu NC film and the proximal AuNPs.Upon the occurrence of the hybridization with its complementary DNA(ssDNA2),an ECL enhancement(on)occurred owing to the interactions of the excited CdS:Eu NCs with ECL-induced surface plasmon resonance(SPR)in AuNPs at large separation.Thrombin could induce ssDNAl forming a G-quadruplex and cause the AuNPs to be close to CdS:Eu NCs film again,which resulted in an enhanced ECL quenching(off).This "off-on-off"system showed a maximum 7.4-fold change of ECL intensity due to the configuration transformation of ssDNA1 and provides great sensitivity for detection of thrombin in a wide detection range from 50 aM to 1 pM.3.An electrochemiluminescence resonance energy transfer system for ultrasensitive detection of prostate-specific antigenAn ECL-RET system based on CdS:Eu NCs and Ru(bpy)32+-doped silica nanoparticle(RuSi)was designed for ultrasensitive detection of prostate-specific antigen(PSA).The system consists of an CdS:Eu NCs film on glassy carbon electrode(GCE)as ECL emitter and a sandwich-type immunocomplex formed by the primary antibody,PSA and the RuSi-tagged second antibody.This system showed a maximum 4.8-fold enhancement of ECL intensity around 620 nm due to the efficient ECL-RET and high Ru(bpy)32+ quantum yields.With the benifit of the signal amplification of RuSi and the specific antibody-antigen interactions,this ECL-RET system could sensitively respond down to 1.0 fg ML-1 PSA.The ECL intensity decrement was logarithmically related to the concentration of PSA in the range from 1.0 fg mL-1 to 1.0 pg mL-1.